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Low battery code for PIRs

Getting the motion code is easy. But I have 3 new motion sensors and I started to notice unknown 433Mhz codes. Most likely for low battery after a few months of operation.

I can not find a pattern and they are very different from the motion codes. Also, I have 433Mhz smoke detectors…not sure if they send low battery codes too.

Does anyone know the formula for calculating the low battery code based on the regular code? Somehow the original alarm panels can do that.

What brand/type are PIRs?

Using RF or PiLight module?

RF 433Mhz

I found this

but the codes are not like that at all

I only have P819 and P829. While P819 doesn’t send low battery code, the P829 does.

With RF gateway, code sent for low battery is 5 point higher than the regular one: say trigger code is 13399178 then low battery is 13399183 (I’m unsure if PiLight reports the same values).

I don’t know if the low battery code for P831 follow the same logic as for P829 as the powering has stepped down (P819 uses 3xAAA then P829 2xAAA although it is advertised as an upgrade on the P819 and P831 even further); however, I suggest (case a stabilized power supply capable of accurate measurement is not available) to test the codes with known good and discharged batteries and check the differences.

Also, if not a large inconvenience, you could power the sensor with the microusb connector which would keep the battery as backup case of power failures (I have several P819s powered with microusb and the batteries are as good as new 3 years after).

Yea I will have to experiment a little bit. I asked the seller about the codes but it was “a secret”.

I charged two of them but I till get more then one unknown code.

Do you know if these send low battery too?

I will post my findings later

I don’t know but I can test it as I have a similar unit (mine wasn’t branded but seems very much like this) and also a variable power supply.

Hi,

(sort of) good news.

The device only sends the payload when activated by smoke or by the test button and it’s the same code always. However, the length is different based on the voltage: starts at 513 at 9 V and increases up to 561 at 4 V (4 V is the cut-off voltage and I assume it takes a longer time to drive the circuit with a lower voltage). A sensor can be set to monitor the length topic in addition to the payload topic to trigger when its value is something like above 540.

Anyway, when below 6 V the sensor emits a faint beep after each 40 seconds.

9V:
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/protocol', ... (1 bytes))
1
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/bits', ... (2 bytes))
24
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/length', ... (3 bytes))
513
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT', ... (7 bytes))
1168723

7.5V:
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/protocol', ... (1 bytes))
1
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/bits', ... (2 bytes))
24
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/length', ... (3 bytes))
533
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT', ... (7 bytes))
1168723

6V:
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/protocol', ... (1 bytes))
1
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/bits', ... (2 bytes))
24
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/length', ... (3 bytes))
546
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT', ... (7 bytes))
1168723

4V:
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/protocol', ... (1 bytes))
1
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/bits', ... (2 bytes))
24
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT/length', ... (3 bytes))
561
Client mosqsub|5593-hass received PUBLISH (d0, q0, r0, m0, 'home/433toMQTT', ... (7 bytes))
1168723

I can confirm that it sends a code larger by 5 than the normal motion code. However, I also get other unknown codes, that is a little bit terrifying :slight_smile:

The Lithium batteries are 3V and the low battery warning is sent on ~2.3V

I expected rechargeable batteries inside but they are not.

I was looking at those a couple of months ago. Is it true that they don’t recharge from the micro usb port? It’s just for use as wired power?

I am not sure. I was actually thinking that they are rechargeable so I put them on a charger and seems like I stopped receiving unknown codes but I was probably wrong :slight_smile:

I ordered rechargeable 2450 batteries and it will take some time till I need to charge them. Probably external charger will do the work.

It is ugly to use them on wall with micro usb cable. But there is plenty of space to drill a hole in the backside and connect a cable from behind.

They do not reach more than 5-6 meters I think. That is the only con, so they are not perfect for presence detection in a big room, but if you want to have burglary sensor it should be fine (433 wireless is not very secure).

If you can check the battery voltage before, and then after a few hours with the cable connected, that would be great.
Otherwise, I’d appreciate it if you could update here once they naturally need recharging. I like the asthetics of those, but like you said, the cable kinda ruins it

I mostly use 2 sensors per room as it’s not always possible to place a single one in ideal position to cover the entire area. Also, there are rooms with non-standard shape (i.e L shape or a large object blocking the sensor) which could not be covered by a single unit (even if it would have a 15-20 m range).

Some of the more expensive products use advanced filters to reduce false positives (like the ones advertised as pet immune); however, the sensor’s cell for PIR sensors is basically the same for most products regardless of communication technology used (433Mhz/Zigbee/Z-wave).

Sure, I will let you know. I have the batteries now. If I use them with cable I would drill a hole from the back side and solder it directly to the battery contacts :slight_smile:

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