A duress button is an example of a "Dry Contact" device. Dry contact is a synonym for 'no voltage'. Since to detect that the push button is closing, we aren't needing to provide any power. We are just detecting when there is a closed circuit, and when there is an open circuit.
We set up with a "Normally Open" push button switch, one side connected to one of the 3 Digital Inputs and the other to ground.
To set up a panic/duress button in the G120, we use either of the 6 digital inputs available. The digital input lines are colour coded in the 24 wire harness- G120 Harness Definition
- Digital Input 1: Pin 16 - Pink
- Digital Input 2: Pin 17 - Blue
- Digital Input 3: Pin 18 - Green/Black
- Digital Input 4: Pin 19 - Brown
- Digital Input 5: Pin 4 - Brown/Blue
- Digital Input 6: Pin 5 - Violet/Red
In this configuration, when the button is OFF (switch open) it is
- Not pressed
- An open circuit,
- And there is no complete path from the input to ground.
When the button is ON (switch closed) it
- Is pressed
- Closes the loop.
- Connects the input to a low signal (GND)
The configuration would be:
- Bias resistor set to 'pull up'
- When the button is not pressed (OFF) and nothing is connected to the input, the input is held high (so we consider this level 'off' (active level = low)
- The Active Level is set to low
- When the button is pressed (ON) the input is pulled to ground.
- The digital input is considered on when the button is pushed.
- We want immediate notification of duress button pushes, so we set Log on Active and Upload on Active to Yes.
Duress Alerts over Iridium
The G120 is able to be used as an Iridium Hybrid device. When connected to an Iridium edge - it will fall back to Iridium when out of cellular coverage. See G120 Iridium Set Up and Operation
Only a subset of device data is sent via Iridium to save on data costs. By default digital input status/changes aren't sent. The specific input(s) to be sent are controlled by a change mask in parameters
The Log on Active mask is a bit mask. In a bit mask any values of '1' we keep, and '0' we discard.
So to allow Digital Input 1 through (kept), in binary this is 0010 = 2 in decimal.
To allow digital input 1 and 2, we have 0110 = 6.
Alerts in Telematics Guru
Please see the instructions here on how to set up Panic/Duress Alert on Telematics Guru
Alerts in Third-Party Platforms
When the state of a digital input changes a record will be sent with Log Reason 9 - Digital Input Changed. Then to determine which input has changed, Field ID = 2: Digital Data contains the state of all digital inputs.