Access control system, what's going on?

The access control system should be one of the intelligent hardware systems that we have the most contact with in our daily life, but have you ever thought about it, what is its principle? In this article, the author tries to popularize the access control system for us, hoping to help you.

One day when I went out from the company, I suddenly became curious about the remote control access control: why can I press the physical remote control to control and open the glass door?

There may be a basic principle here: when the button of the remote control is pressed, the built-in battery power is converted into a radio signal, and the receiver is converted into an electrical signal to control the door opening and closing through the electrical energy.

But if you think about it further, the water here should be deeper.

1. Usage scenarios

The access control system encountered in current life includes the following scenarios:

(1) Access to office buildings and companies

(2) Residential communities, unit doors

(3) Electronic locks for hotel elevators and room doors

(4) Access to railway stations, high-speed rail stations, and airports

Of course, there are some other scenarios, such as government agencies, schools, hospitals.

It can be combined with monitoring equipment to realize channel capture and event warning. It can be combined with the door machine Android APP to realize video intercom unlocking.

In short, it can be confirmed that the access control system is closely related to security management.

Second, product introduction

The evolution of the access control system is as follows: from key unlocking, to swiping the card to open the door, and then to forming an IoT access control system integrating software and hardware.

1. How to open the door

There are three categories of users: building personnel (owners/employees/guests), visitors, and strangers.

Common ways to open the door include: access control card, door opening button, remote control, face recognition, password verification, fingerprint recognition, APP or applet.

1.1 Access card + card reader

Access cards will be used to enter and exit some communities, such as:

Or office employees also need to swipe their cards to enter, such as:

The basic principle of contactless IC access card (smart card):

A. LC series resonant circuit: Inside the non-contact IC card, there is an LC resonant circuit composed of inductor L (antenna coil) and capacitor C (from the IC card chip). This circuit induces an electric current after the RF reader emits electromagnetic waves, and the current oscillates back and forth between the inductor and the capacitor, forming an electromagnetic oscillation. When the frequency of the electromagnetic wave emitted by the card reader is the same as the resonance frequency of the LC circuit, the resonance effect occurs.

B. Accumulation of charge to form voltage: When the LC circuit resonates, the capacitor C will be repeatedly charged and discharged under the action of alternating current, resulting in voltage. This voltage is the source of the power supply of the IC card, which can drive the chip in the IC card to run.

C. Transmitting or receiving data: Driven by voltage, the chip of the IC card can transmit the information stored in it in the form of electromagnetic waves. At the same time, the chip can also receive signals from the card reader and read or write data.

D. Authentication and control: The card reader obtains the card information and transmits it to the controller for authentication - after the controller verifies, it controls the switch of the electric lock, and records the entry and exit card records at the same time. Some high-security cards also reverse-validate the reader.

In the case of RF card readers (no need to insert a specific reader slot): an alternating current passes through a conductor, and an alternating electromagnetic field is formed around the conductor, forming high-frequency electromagnetic waves with a frequency higher than 100kHz and long-distance transmission capabilities.

Mobile phone simulates physical access control card:

Provided that the phone supports NFC and the access card is not encrypted. NFC stands for Near Field Communication, which is a short-range, high-frequency wireless communication technology that transmits data through electromagnetic induction. In one-to-one communication, the party that initiates the connection is the initiating device and the other party is the target device, and both the initiating and destination devices support both active and passive communication modes.

A. The mobile phone copies the access control card to store the information. The NFC mobile phone acts as a card reader to send out RF signals, and the access control card acts as an RFID receiver to absorb the RF signal and generate current, which in turn drives the identification information back to the transmitter mobile phone. The mobile phone stores this information and realizes the function of copying the access control card.

B. The mobile phone simulates the access control card and opens the door. The access control card reader sends out a radio frequency signal, the mobile phone simulates the access control card to receive the signal, and the induced current drives the identifier information back to the electric lock in the form of electromagnetic waves to open the door.

For example, the access control card copied by Huawei mobile phone:

1.2 Remote Control

The access control remote control is equipped with a radio transmission module inside, when the user presses the button, the transmission module will convert the access switch signal into a radio wave signal and transmit it. This signal will be received and decoded by the access control device, which will then determine whether to open or close the door based on the decoded signal.

There are two main frequencies of commonly used access control remote controls: 315MHz and 433MHz.

A. 315MHz: stable transmission signal, long transmission distance, small interference, widely used in the access control market.

B. 433MHz: strong penetration, able to pass through some obstacles, such as walls, soundproof doors, etc., and the transmission distance is also relatively long, but it is greatly affected by interference.

1.3 Face Recognition

Facial recognition technology has also become widespread. Taking the industry's well-known 3D visual perception overall technology solution provider [Obi Zhongguang] as an example, it provides a 3D face-brushing door lock access control solution. Face recognition technology includes: 3D face recognition algorithm, face live detection, etc.

(1) 3D face recognition algorithm

3D sensors, using stereo vision technology, can perceive three-dimensional space. Among them, stereo vision uses two or more cameras (like human eyes) to obtain images of the target object from different angles, and then through computer algorithms, the shape and position of the object in three-dimensional space are inferred.

3D face recognition is the process of scanning the face of the person being detected to form a 3D model containing facial features, which is compared with the 3D model already stored in the database. If the comparison result exceeds the preset threshold, the detected human face is considered to be consistent with the real human face stored in the database.

(2) Face in vivo detection

Common scenarios are interactive random motion detection, such as opening the mouth, blinking, and turning left and right.

In access control systems, non-interactive methods are generally used, such as near-infrared face liveness detection.

A. Near-infrared light irradiation: Shooting the face through the camera, and irradiating the face with near-infrared light at the same time, because the near-infrared light is invisible to the human eye, it will not cause discomfort to people.

B. Reflected light detection: The reflection of near-infrared rays on the skin and eyeballs of human faces is different, and the reflection of near-infrared rays on living and non-living individuals (such as photos, videos, and fake faces) is also different.

C. Liveness detection: The camera captures the reflected near-infrared light and compares it with the facial features of the living person to determine whether it is alive.

The optical flow method, which belongs to the field of computer vision, can further improve the accuracy of face live detection. Optical flow is the effect of pixels moving in a time-series image, and the slight movements of the face (such as blinking, smiling, etc.) will change the pixel value of the image, and these micro movements can be detected by optical flow method. If, during observation, the pixel value of a face undergoes a normal change consistent with natural facial micro-movements, then the face is more likely to be judged to be alive.

1.4 APP or applet + Bluetooth

Similar to shared bicycles, they are unlocked through Bluetooth. Here's how it works:

A. Bluetooth communication. Bluetooth is a short-distance (generally less than 10m) wireless communication technology (personal area network), which is controlled by a master device and composed of one or more slave devices, forming a point-to-point, point-to-multipoint network structure. It operates at around 2.4GHz, which is a free frequency band in the world that does not require a license (but is regulated). Reduce radio interference by using frequency-hopping spread spectrum (where both sides of the communication skip to a certain frequency), and Bluetooth pairing with a pairing code to ensure privacy and security.

B. Application control. Through the APP or applet on the mobile phone, the user can send instructions to open or close the door lock. These instructions are encoded into a special Bluetooth signal, which is then sent out by the phone's Bluetooth module.

C. Door lock receiving. The door lock itself also has a Bluetooth module that can receive Bluetooth signals. Once the unlocking or latching instruction is received from the APP or applet, the electronic system of the door lock will activate the mechanical switch accordingly to unlock or latch.

In addition, the APP/applet of community door opening is drained through relatively rigid door opening service + property service, and expands community services such as cleaning and pest control, home appliance cleaning and maintenance, and waste recycling.

For example, [Neighbor Door Opening] was established in 2015, and as of 2023, it has served more than 60,000 communities, more than 12,000 cooperative properties, more than 28 million mobile phone door users, and 3.2 billion door openings. It's a relatively strong traffic entrance.

1.5 Video intercom

Two-way communication of image and sound is realized. Principles include:

A. Image transmission. The visitor asks the property or occupant to open the door through the doorbell, and the outdoor camera begins to take images, convert them into electrical signals and transmit them to the room, decode them and display them on the screen.

B. Audio transmission. Indoor and outdoor two-way voice communication can be realized, because there are microphones and speakers indoors and outdoors, and the microphones collect speech and convert it into electrical signals, transmit it to the other party and then decode it, and play it out through the speaker.

Hikvision, which ranks the top in the global security field, sells a one-to-one (an indoor unit and an outdoor unit) video intercom access control system on JD.com, which is about 800 yuan. The picture below shows Hikvision's indoor unit door opening:

Among them, the design of outdoor units includes:

A. High-definition infrared night vision (120° wide-angle lens): Infrared night vision uses the infrared thermal radiation signal emitted by the target, which is converted into an electrical signal by the infrared detector, and forms an infrared picture visible to the human eye after signal amplification, processing and imaging. Wide-angle lenses, on the other hand, have a shorter focal length and a larger angle of view, so that the field of view is wider.

B. Waterproof design of outdoor unit (IP65): IP65 stands for dustproof level 6, which completely prevents dust intrusion, and waterproof level 5 to prevent jet water intrusion.

2. Access controller

It is used to control the opening and closing of doors in a certain area. The heart of the access control system is: the control panel.

Assume the function of processing information and decision-making. The data sent by the card reader or other devices (fingerprint scanners, face readers) is processed by a microprocessor to make decisions based on preset rules. Through memory, it stores running programs, access control rules, and records traffic logs, etc., of course, in the case of networking, local storage may be weakened. In complex access control systems, communication with the management system via Ethernet or WiFi is also required.

If there is a door, swipe the card when you enter the door and press the button when you go out, the controller can only connect one card reader for each door, which is called a one-way controller.

If a door, swipe the card when you enter the door and swipe the card when you go out (you can also connect the door button), each controller can be connected to two card readers for each door, one is the door reader, and the other is the card reader when you go out, which is called a two-way controller.

Hikvision's access controllers are as follows:

Wiring of the access controller:

3. Access control power supply

The main function of the access control power supply is to convert the standard civil voltage of 220V AC power into 12V (general) DC power required for access control, and provide power support for the controller, card reader, electronic lock, building intercom and other equipment in the access control system.

At the same time, the access control power supply also has functions such as over-current protection, over-voltage protection and short-circuit protection to ensure the safety and stability of the system.

4. Access control gates

The access control turnstile is a channel management device that controls the entry and exit of personnel. Only after the identification is completed can the passage be allowed.

4.1 Turnstile Type

A. Three-stick gate. We often see it in subway stations, gymnasiums, etc.

B. Wing gate. If you are in an office building, after verifying your identity, you will open the "wings" on both sides

C. Full-height turnstile. For example, at the exit of buying tickets in the community and high-speed rail. It can provide better security and is not easy to cross or drill through.

4.2 Turnstile Functions

The access controller can be used to implement a variety of functions, such as:

A. Multi-door interlocking. The main thing is that multiple doors form a linkage, and only one door can be kept open. It is not possible to open multiple doors at the same time to form a passage to prevent non-staff members from flowing unimpeded. In case of special circumstances such as fire, the multi-door interlock can be lifted and the normally open state can be maintained.

B. Anti-submarine return. For two-way card swiping access control, it is an anti-tailgating mechanism, requiring personnel to verify that the access record is strictly corresponding to one entry and one exit. For example, if a person enters by swiping the card or fingerprint (without leaving the record), the IC card cannot be verified again by handing it to someone else.

5. Linkage system

5.1 Ladder Control

Elevator control, that is, the elevator controller, controls the operation of the elevator and meets the needs of elevator passengers. For example, when the passenger presses the call button, the elevator control system will select the most suitable elevator to serve according to the passenger's location and the current operating status of the elevator. When the elevator is in operation, the elevator control system will control the opening, closing, rising and descending of the elevator according to the height of the floor and the speed of operation.

At present, many chain hotels, residential buildings, and office buildings are also linked to access control and elevator control. That is, after entering the elevator, you need to swipe the IC card again to identify yourself, and automatically or manually select the floor with the specified authority.

For example, Hikvision's elevator control host can realize the control of access rights at up to 128 layers, and support multiple authentication methods such as card swiping, fingerprinting, card swiping + password, etc.

5.2 Attendance

For schools and office buildings, attendance issues are involved.

DingTalk has launched smart hardware products, including face/fingerprint attendance access control machines. Employees brush their faces, automatically open the door after recognition, and complete attendance clocking in and out synchronously.

The following is that the DingTalk administrator can configure the attendance management system to add a smart attendance machine.

5.3 Visitor Management

Visitor machines have also become popular, providing reservations and registration for visitors. When a visitor enters the turnstile with a pass, the access control system is connected to achieve authentication, access control (including accessible areas and valid hours).

5.4 Fire Alarm

Access control is set up in the evacuation passage to affect escape. When a fire occurs, the fire alarm system sends a signal, and the access control system executes the opening or closing of the designated gate to ensure the normal evacuation and escape of personnel.

The electric push rod lock has the functions of access control and fire escape, and realizes the integrated management of safety and elimination. It is very suitable for fire evacuation channels such as shopping malls, supermarkets, and office buildings. Unauthorized people push the escape door lock, start the voice beep alarm and play "This is the escape exit, please evacuate quickly, WO, WO, WO", and open the door to go out. In the event of a fire, the escape door lock receives a linkage signal, and the voice buzzer alarm is activated to play "This is the escape exit, please evacuate quickly +, WO, WO, WO", and guide the personnel to escape from here.

Third, the access control industry

1. Market size and growth rate

According to the report of Essence Securities Research Center: the average annual compound growth rate of the access control market is okay, at about 13%.

However, the access control industry is a relatively subdivided track, and the total scale is not large (

2. Development status

The barriers to entry are not high, the industry is uneven, and the industrial concentration is not high. Under the homogeneous competition, there is a close price war and the interest rate is relatively thin.

The whole industry is moving towards integration and giving full play to the advantages of branding and collectivization. At the same time, the related technology of the access control system has been relatively mature and has entered a large-scale development stage, integrating with security, finance, transportation and other fields.

The big players in the industry include Hikvision in the security field, DingTalk from office software, Dahua Technology and Entropy-based Technology, which are listed on A-shares, and Qinlin Technology from community management.

3. Access control business of Lifang Holdings

The gross profit of Lifang Holdings' intelligent access control system ≥ 60%, which should be very high. The company has a 20-year history and is listed on the Beijing Stock Exchange, which is also a relatively large player.

The main customer structure of Lifang Holdings is as follows, and the sales revenue of the top 5 customers is accounted for

In 2022, Lifang Holdings' R&D expense ratio will reach 16.3%, of which the access control-related technologies are as follows:

Fourth, write at the end

1. Access control products have developed from simple hardware to an Internet of Things system integrating software and hardware, integrating weak current system engineering and computer technology.

2. The access control industry belongs to the field of security, and is moving from homogeneous competition to branding and large-scale development, so as to provide integrated solutions and enterprises to obtain higher gross profit margins.

This article was originally published by @马老师 on Everyone is a Product Manager. Reproduction without the permission of the author is prohibited.

The title image is from Unsplash and is licensed under CC0.