Hello all,

I have an alarm system that communicates over 319.9mhz. I'm curious if anyone has intercepted signals like these before and if so, where did you get your receiver? I'm unable to find one at that mhz.

If you are in the US, then it is probably 315MHz (or it is supposed to be 315MHz :wink: ). How did you measure the 319.9MHz ?
Could you open a detector to see what chips are inside ?

It is actually 319.5mhz. I had a typo in the subject. I read it from the chip on the board. I believe it is the NX-408 version. Page 12 on this PDF has the Mhz.

Compatibility: NX-8 control panel
Frequency: 319.5 MHz (NX-408, NX-416, & NX-448)
433 MHz (NX-408-I, NX-416-I, & NX-448-I)
Required Power: 12.0 VDC (provided by panel)
Current Draw: 20 mA maximum
Operating Temperature Range: 32° to 120°F

The 433 MHz is normal for Europe. The 319.5 MHz is perhaps within the legal range of the 315 MHz band.
All receivers are 315MHz or 433MHz. The very cheap receivers have a coil with a core to tune the frequency.

The document is from 1998, that means that the protocol is probably not encrypted. It might be an own protocol, but it also might be a protocol similar to 2272 / 2262 tri-state format.
Did you open a transmitter (a detector, a sensor) ? can you identify the chips ?

The RCswitch and fuzzillogic libraries can read the 2272 / 2262 protocol. I used RCswitch in the past, but I have moved to fuzzillogic.


Use a cheap receiver, one of those with a coil with green plastic and red lacker on top : http://www.ebay.com/sch/i.html?_nkw=315mhz+kit
Connect an attenuator to the data signal, perhaps 100k resistor to data, 10k resistor to GND. Connect the attenuated signal to the computer line-in, also connect GND. Use Audacity to capture the received signal.
It should look something like this : http://hblok.net/blog/posts/2012/09/02/home-automation-on-433-92-mhz-with-arduino/
Move the transmitter further away, 20 meters, 30 meters, and tune the coil with a plastic screwdriver.

I read this in another document:
Frequency: 319.508 MHz
Transmitter frequency tolerance: +/- 8 khz
Bandwidth : 24 khz
Modulation type: Amplitude shift key (ASK)
But I can't find what kind of protocol for the modulation is used.

If you show us the signal from Audacity, you will publish how to disturb your alarm system :confused:

I just saw this post and even if it's a very old one I want to put my 2 cents.
First of all 319.5 MHz is the frequency used by GE-Interlogix sensors.
This is a former military frequency, used in all the sensors made by the company since the 80’s. There are literally millions of these sensors in use, each with a unique transmitter ID. The communication between sensors and panel is not encrypted.

The sensor employs amplitude modulation and transmits 61 bit or 80 bit ITI protocol.
The duty cycle correction factor will be derived for both 61 bit and 80 bit ITI protocol.
A 61 bit ITI protocol packet begins with an “ON” time of 854 mS, each bit has an “ON”
time of 122 mS, and one bit has an additional 244 mS. The total “ON” time of a single
packet is:
854 mS + 61 * 122 mS + 244 mS = 8.54 mS.
Only one packet is sent in any given 100 mS window for a duty cycle correction factor of:
20LOG(8.54/100) = -21.4 dB
In 80 bit ITI protocol packet each bit has an “ON” time of 122 mS. The total “ON” time of
a single packet is:
80 * 122 mS = 9.76 mS.
Only one packet is sent in any given 100 mS window for a duty cycle correction factor of:
LOG(8.54/100) = -20.2 dB
The maximum allowed correction factor is -20.0 dB.

All this info are available on FCC spec. of the sensor:


I don't know if anyone has succeeded intercepting and decoding the signal coming from these sensors.
I have a Simon XTI panel and I would like somehow to connect it to OpenHAB. I didn't find any document explaining how can i communicate with the panel and trying to hook-up the sensors looks even trickier.

There is a solution now.

Not Arduino based, but the code is in C, and can be ported with some effort.

It is based on Software Defined Radio (SDR).

Basically, you buy this USB RTL-SDR dongle, then download this repository (which is a fork of rtl_433) from Github.

You compile the code, then run the following command:

rtl_433 -f 319500000 -R 98 -F json

-f is the frequency for these sensors
-R is the ID for Interlogix, the maker of these sensors
-F is the format of the generated data stream

With json, you can then pipe the output to MQTT, and use the data on the MQTT server whichever way you want.