door "sensor" that detects my body

[kenny1999]

I am not living in a very modern building and the budget of the management company is not high so I think the technology employed shouldn't be something new. The public entrance door is normally closed and locked and it can only be unlocked when I put my hand close to the door "sensor" then it will detect my hand and unlock the door, but if I touch the "sensor" it will not unlock the door and doesn't show any response. What is the general working principle of such device?

I don't know if it's actually a sensor so I use quote and quote in the above context.

Edited October 8, 2022 by kenny1999

[TheVat]

Detect your hand?  Not clear what that means.  Your door sensor reads the pattern of your palm?  Or in some way makes a positive ID of your hand?  This sure doesn't sound low budget, if that's what you are describing.  Quite sophisticated in fact.  Like Fort Detrick Biohazard Lab sophisticated.  

[kenny1999]

5 minutes ago, TheVat said:

Detect your hand?  Not clear what that means.  Your door sensor reads the pattern of your palm?  Or in some way makes a positive ID of your hand?  This sure doesn't sound low budget, if that's what you are describing.  Quite sophisticated in fact.  Like Fort Detrick Biohazard Lab sophisticated.  

OK, my language problem, Let's make it clear, I mean, it detects ANY part of human body and unlock the door immediately, there is nothing about fingerprint or ID, it's not a security door, anyone who puts their hand (or any part of their body) near the "sensor" then it will unlock the door (but it won't unlock if you touch on it, it only works when your hand puts near it but not too far away, and not touching it). I only want to know the working principle of such device.

[Sensei]

To implement such functionality sound waves can be used.

Buy an Arduino and an ultrasonic distance sensor. Here's a tutorial on how to make it work:

https://create.arduino.cc/projecthub/abdularbi17/ultrasonic-sensor-hc-sr04-with-arduino-tutorial-327ff6

It is used by automatic robots, for example, that clean the floor or to light up rooms when someone enters them.

Edited October 8, 2022 by Sensei

[TheVat]

36 minutes ago, kenny1999 said:

OK, my language problem, Let's make it clear, I mean, it detects ANY part of human body and unlock the door immediately, there is nothing about fingerprint or ID, it's not a security door, anyone who puts their hand (or any part of their body) near the "sensor" then it will unlock the door (but it won't unlock if you touch on it, it only works when your hand puts near it but not too far away, and not touching it). I only want to know the working principle of such device.

 

OK, thanks, I see now.  Normally, automatic doors use a light beam that is interrupted by a body.  Heat sensors don't work well, because weather causes too much variation in both air temperature and in hand temperature.  So, as @Sensei says, it may use sound, so touching it would mess it up (make it "deaf") and it would not work.

[Phi for All]

54 minutes ago, kenny1999 said:

OK, my language problem, Let's make it clear, I mean, it detects ANY part of human body and unlock the door immediately, there is nothing about fingerprint or ID, it's not a security door, anyone who puts their hand (or any part of their body) near the "sensor" then it will unlock the door (but it won't unlock if you touch on it, it only works when your hand puts near it but not too far away, and not touching it). I only want to know the working principle of such device.

I still don't understand. Any kind of proximity sensor is part of a security system, which can be expensive. Why lock a door, ANY door, if EVERYBODY who puts any part of their body in front of the sensor can open it? It's not that much more expensive to add some kind of RFID device like a key fob that the sensor recognizes as belonging to a resident. 

As to the sensor, they have a range, which in your case must be from a few inches to a few feet. You can't trigger it from farther away, and touching it may be too close. It's still weird that your building would buy an electronic lock with a sensor but not include the extra steps to secure the system. Does this door lead to a lobby area, or does it just give access to the halls and stairs?

[swansont]

1 hour ago, kenny1999 said:

OK, my language problem, Let's make it clear, I mean, it detects ANY part of human body and unlock the door immediately, there is nothing about fingerprint or ID, it's not a security door, anyone who puts their hand (or any part of their body) near the "sensor" then it will unlock the door (but it won't unlock if you touch on it, it only works when your hand puts near it but not too far away, and not touching it). I only want to know the working principle of such device.

It could be an IR source and detector. You only get enough return when an object is nearby. If you touch it, you’re blocking the sensor. 

14 minutes ago, Phi for All said:

As to the sensor, they have a range, which in your case must be from a few inches to a few feet. You can't trigger it from farther away, and touching it may be too close. It's still weird that your building would buy an electronic lock with a sensor but not include the extra steps to secure the system. Does this door lead to a lobby area, or does it just give access to the halls and stairs?

We have these at work for ADA compliance - the door opens automatically rather than opening by hand or pushing a button. Not security-related, as such.

[Phi for All]

1 hour ago, swansont said:

We have these at work for ADA compliance - the door opens automatically rather than opening by hand or pushing a button. Not security-related, as such.

Inside a building, they make a lot of sense. I can see them being used even more now with health safety concerns. Cuts down on objects we have to touch that lots of other people had to touch. 

[swansont]

35 minutes ago, Phi for All said:

Inside a building, they make a lot of sense. I can see them being used even more now with health safety concerns. Cuts down on objects we have to touch that lots of other people had to touch. 

These are main entrance, though it’s a gated community, and we have people at the gate. 

[kenny1999]

7 hours ago, TheVat said:

 

OK, thanks, I see now.  Normally, automatic doors use a light beam that is interrupted by a body.  Heat sensors don't work well, because weather causes too much variation in both air temperature and in hand temperature.  So, as @Sensei says, it may use sound, so touching it would mess it up (make it "deaf") and it would not work.

Light beam? Sound wave? Can I have some understanding of how it works? Does the device continuously emit light wave and when someone get close to it, it will interrupt the light wave? 

I have some physics knowledge but not too much.

6 hours ago, swansont said:

It could be an IR source and detector. You only get enough return when an object is nearby. If you touch it, you’re blocking the sensor. 

We have these at work for ADA compliance - the door opens automatically rather than opening by hand or pushing a button. Not security-related, as such.

IR source and detector? Can I have some brief understanding of how it works? Yes, when I touch it, it doesn't work, when I am far from it, it doesn't work. Only when I put my hand close to it (but not touching it), it works. Is it using sound wave or light wave or something otherwise? I don't think there is any emitter around, does it itself emit light wave or sound wave so that when I get close to it, the wave is interrupted? 

P.S. As I said, this is not a door for security, it's in the public area, and our building isn't very modern. I only wish to learn about the working principle behind.

[Janus]

I'm wondering if it is capacitive. Placing your hand near it alters the capacitance, which sensed as a frequency change in the circuit.  Touching disrupts the circuit. Just a wild guess.

[swansont]

18 hours ago, kenny1999 said:

 

IR source and detector? Can I have some brief understanding of how it works? Yes, when I touch it, it doesn't work, when I am far from it, it doesn't work. Only when I put my hand close to it (but not touching it), it works. Is it using sound wave or light wave or something otherwise? I don't think there is any emitter around, does it itself emit light wave or sound wave so that when I get close to it, the wave is interrupted? 

P.S. As I said, this is not a door for security, it's in the public area, and our building isn't very modern. I only wish to learn about the working principle behind.

IR = infrared light, so you can’t see it. As I said, you only get enough return when an object is nearby; the beam expands with distance. If you touch it, you’re blocking the sensor, so it won’t trigger

[kenny1999]

On 10/10/2022 at 4:36 AM, swansont said:

IR = infrared light, so you can’t see it. As I said, you only get enough return when an object is nearby; the beam expands with distance. If you touch it, you’re blocking the sensor, so it won’t trigger

but why when I put my hand near it, it will work correctly and does not block the sensor?

[swansont]

On 10/17/2022 at 12:54 AM, kenny1999 said:

but why when I put my hand near it, it will work correctly and does not block the sensor?

Because you aren’t blocking the sensor.

[kenny1999]

On 10/20/2022 at 9:48 AM, swansont said:

Because you aren’t blocking the sensor.

I mean, I wish to know the principle. What is the sensor doing? Emitting infrared or other radiations? However, I think light or radiation could easily pass through our body!

[Ghideon]

47 minutes ago, kenny1999 said:

I mean, I wish to know the principle. What is the sensor doing? Emitting infrared or other radiations? However, I think light or radiation could easily pass through our body!

There may be two parts; emitter and receiver, placed close together. An IR emitter keeps transmitting infrared light and when any object comes near, it is detected by the receiver by monitoring the reflected light from the object. If you are far from the sensor the emitted IR light reflected from you will not be registered by the receiver. By blocking the sensor there is no path for the emitted IR light to reach the receiver; the IR light will not be reflected to the receiver.

Below is a picture, note the emitter and receiver: IR LED and photo diode. 

(Source: links to https://www.instructables.com/Easy-Infrared-Proximity-Sensor/ The page describes the principle in more detail) 

You can google for "ir proximity sensor".

[swansont]

7 hours ago, kenny1999 said:

I mean, I wish to know the principle. What is the sensor doing? Emitting infrared or other radiations? However, I think light or radiation could easily pass through our body!

An IR source and a sensor. The IR source emits light. The sensor detects reflected light that returns to it. The beam expands, so there is less light as the distance increases, which means it won’t work if you are too far away. 

You can’t see through people, so no, light does not easily pass through our body.

[kenny1999]

On 10/22/2022 at 5:38 PM, Ghideon said:

There may be two parts; emitter and receiver, placed close together. An IR emitter keeps transmitting infrared light and when any object comes near, it is detected by the receiver by monitoring the reflected light from the object. If you are far from the sensor the emitted IR light reflected from you will not be registered by the receiver. By blocking the sensor there is no path for the emitted IR light to reach the receiver; the IR light will not be reflected to the receiver.

Below is a picture, note the emitter and receiver: IR LED and photo diode. 

(Source: links to https://www.instructables.com/Easy-Infrared-Proximity-Sensor/ The page describes the principle in more detail) 

You can google for "ir proximity sensor".

Blocking the sensor? Did you mean when I touch it so there is no air in between, then it will block the sensor and doesn't work?

[swansont]

1 hour ago, kenny1999 said:

Blocking the sensor? Did you mean when I touch it so there is no air in between, then it will block the sensor and doesn't work?

You are preventing light from reaching the sensor.

[kenny1999]

4 hours ago, swansont said:

You are preventing light from reaching the sensor.

My fingers are never big enough to cover the whole button, but it still works. Why?

[swansont]

7 hours ago, kenny1999 said:

My fingers are never big enough to cover the whole button, but it still works. Why?

The sensor is smaller than that. The “whole button” would also include the light source and the housing.