Question:
my inlaws have a security system with a couple fire sensors built-in to the circuit. Its about 14 years old, and one of the fire sensors has gone kaput, and thinks there is a fire all the time.... preventing use of the rest of them since they have to deactivate the system. I took a look, but didnt see any fuses or batteries that would be an easy fix. They already installed separate fire alarms to get back up to code, so I was thinking about shunting around the bad sensor. there are four wires to the alarm: red, green, black, yellow. looks like phone wire. Any ideas on whether I could simply disconnect them ALL, or wire some together to shunt around the bad sensor, and leave the rest of the system up. If it would help, I could go up and take a digital picture of the circuit.

Answer: Just replace the smoke detector, it's expired. They have a carbon cell (or something?) that ages and fails to sense correctly after many years of service. My parents had the same problem, after about 10 yrs one smoke detector went out then the other followed within 2 months time. So you might consider replacing the others at the same time OR at least warn your in-laws about the possibility of future false alarms. With my parents place I simply unplugged the bad detector until it could be replaced. I have no idea if your system will allow that.