Fire Station, Speaker Output To Trigger Relay?

I am trying to engineer something for a local volunteer fire station. they are wanting a few very small overhead 12v led lights to come on for a few minutes when there alerting system goes off. all they have now is a motorola radio system with a positive/negative speaker wires coming out of the back. is there a way to use the positive speaker wire to activate a relay which is on a small timer, that will turn some small lights on for about 3 minutes before they automatically turn off?

http://www.circuitdiagram.org/audio-activated-relay-switch.html You can use the above along with a DEI timer module. I do not know the part number but I am sure somebody here can help with that.