The BLUE wire and the GREEN wire

[radargeek]

A bit confusing, as it says 1 channel, but shows 2 x VCC inputs, which I originally assumed would be for a second channel ?

It also says 5V relay, whereas mine, you could specify various input voltages, 12V, 24V etc. I'm not upto speed on electronics, so will let one of the others chime in !

It has two Vccs because of the isolation circuit (opto-coupler). For your application they can be connected together. The Ctrl input would go to the relay wire on the ALP, and Vcc would go to a 5V supply (you may have to use a 7805 or 78L05 regulator or something). If you're using an Arduino it would have a 5V supply on-board.

A circuit with a 12V relay and a transistor would be simpler to implement since you wouldn't have to provide a 5V supply.

[winterbrew]

That looks like it will work. The issue is the ALP is sending I believe standard TTL I/O. (+5v). Which is just not enough to drive a relay. Using that device will allow you to drive a relay based on the Vcc on the board triggering when the ALP goes high. Let us know how you make out.

Ok, just did a quick test of the relay - looks like we're in luck

Relay Board Inputs ;

VCC connected to +12V (car battery +ve)
GND connected to earth (car battery -ve)
CH1 connected to the ALP +5V TTL on alert (green wire)

The green LED on the relay comes on during alert, and you can hear the click of the relay activating. It remains activated all the time the alert is being played

Instructions say when relay activates, Normally Open (NO) is connected with COM (there is also Normally Closed (NC)) - confirmed with continuity check on multimeter.

[Mirage]

Ok, just did a quick test of the relay - looks like we're in luck

Relay Board Inputs ;

VCC connected to +12V (car battery +ve)
GND connected to earth (car battery -ve)
CH1 connected to the ALP +5V TTL on alert (green wire)

The green LED on the relay comes on during alert, and you can hear the click of the relay activating. It remains activated all the time the alert is being played

Instructions say when relay activates, Normally Open (NO) is connected with COM (there is also Normally Closed (NC)) - confirmed with continuity check on multimeter.

Great job now just remember whatever you connect is going to stay on during the entire alert as I stated in the op.