Protecting a PIR detector from being abused

[g2c]

Hello,

I want to make a PIR detector based on this module or alike and intend to add means to detect that
1) it had not been snatched: by adding a parallel resistor on the module supply pins and measuring the supplied current
2) it has not been covered: How do one does that??? (i'd prefer avoid using permanent visible light + detection)
Thanks in advance for your suggestions
Guy

 

[cowboybob]

To what device/circuit are you attaching the detector?

 

[Tony Stewart]

Perhaps have two units for redundancy. One hidden better than the other behind IR transparent daylight-blocking plastic filter.

Or have a dummy camera in an active hidden PIR.

 

[cowboybob]

... 1) it had not been snatched: by adding a parallel resistor on the module supply pins and measuring the supplied current...

Add a wire carrying the Vdd on the PIR back (with the other three already in place) to whatever is your monitoring device. Someone snatches the PIR, that Vdd signal will disappear (go to 0VDC, whatever).

 

[g2c]

To what device/circuit are you attaching the detector?

I forgot to mention, the PIRs will be bundled 3 in a a round plastic box -will post picture later- in the middle of the external walls, each directed to another of the 3 windows of each wall. Each bundle will be connected via 8 conductor phone cable to an inhouse board managed by an arduino. As for the presence detection, since the PIRs operate at 3.3V using an LDO and the arduino uses 5V I should be able to sense the presence without using an extra wire:
2 will be used for the power
3 for the info: i'd rather nor OR it to have a better follow up on what's going on
3 reserved for the moment

 

[BobW]

Place an infrared emitter within sight of the sensors. Every few seconds (or minutes), blink the IR emitter, and check that the PIRs sense the signal. If the sensor is stolen or becomes non-functional or the sensor is covered, the test will fail, and your electronics can generate a trouble signal.

 

[dr pepper]

Commercial alarm sensors have a tamper contact on the cover, put a microswitch contacting the table on the bottom of the box and out of sight, if someone lifts the box up the switch actuates and your elctronics detects it, in conjunction with bobs infra red self test your system will be well protected.
Another theft prevention and combined covering up protection would be to use a visible or infra red led and a retroflective strip stuck on a wall in the room, the electronics pulses said led and looks for a reflection, if it doesnt get it then its either covered up or has been moved, but this does mean sticking a retroflective strip somewhere in the room.

 

[g2c]

Place an infrared emitter within sight of the sensors. Every few seconds (or minutes), blink the IR emitter, and check that the PIRs sense the signal. If the sensor is stolen or becomes non-functional or the sensor is covered, the test will fail, and your electronics can generate a trouble signal.

I tried with the air conditioning remote: It is not detected by the pir

 

[g2c]

Commercial alarm sensors have a tamper contact on the cover, put a microswitch contacting the table on the bottom of the box and out of sight, if someone lifts the box up the switch actuates and your elctronics detects it, in conjunction with bobs infra red self test your system will be well protected.
Another theft prevention and combined covering up protection would be to use a visible or infra red led and a retroflective strip stuck on a wall in the room, the electronics pulses said led and looks for a reflection, if it doesnt get it then its either covered up or has been moved, but this does mean sticking a retroflective strip somewhere in the room.

Well, for the anti snatch, the current consumption scheme should reliably do the work without mechanical switches.
For the covering detection system, pulsing an IR emitter directed to one of the three sensors means i have to stick it somewhere on the wall and to power it (preferably with the same controller so it can test the receiver while powering the transmitter) but i made no provision for such a transmitter. I was wandering if i could use a sonic transceiver placed inside the plastic box which would detect if the box is being covered by an object, even a cloth.

As promised, here are the pictures

 

[BobW]

I tried with the air conditioning remote: It is not detected by the pir

A standard IR remote will be near infrared, and a PIR senses far infrared. I would try an incandescent light bulb running at a fraction of its rated voltage. It probably won't be glowing visibly at all when it's at the right wavelength.

 

[crutschow]

A standard IR remote will be near infrared, and a PIR senses far infrared. I would try an incandescent light bulb running at a fraction of its rated voltage. It probably won't be glowing visibly at all when it's at the right wavelength.

It should generate significant long-wave IR when it is glowing a dull red.

 

[g2c]

The solution i adopted is to connect the pir output to an Arduino INPUT_PULLUP. If the pir wire is cut, the signal will remain high. Now, in the debouncing code, i added means to detect 'tooLongHigh' which fires an exception. Incidentally i found that after two years some pirs start generating this exception and need to be replaced