just found this out, but if you need to make cheap heat detectors, the resort to thermal switches. you can find thermal switches in motors, heating elements, and fluorescent light starters. the switches in motors, heaters etc are therm cutouts which open the circuit then they get hot/ heat up. for the therm cutouts, you will need a not gate to invert the signal for the switch to work as a conventional heat detector. for the fluorescent starters, you do not need to hook up any logic gates, but you may need to break the glass envelope to aid in heat exchange. you should also add a heat sink to help in thermal transfer.
some more pics of heat switches that could be used…
Doing this may DESTROY your FACP, You have been warned…
HOW SO?
Big Green, Some people are not the smartest…
Agreed. The chances of a younger user without much real equipment or knowledge trying to make this and frying their panel are high.
^^^ Seen pretty often around here too. :idea: + 
= 
you won’t fry a panel with a thermal switch, it’s not common but also not unheard of to monitor thermal switches on fans on a fire alarm system set up for smoke control. it’s basically a dry contact, opens up when it gets hot, closes again when it cools back off.
Yes, but when some kills there panel, i don’t wanana here about it.
It really is no different than wiring a pull station, it would be just as easy to damage a panel with a real heat detector.
Here are some lower cost N/O thermal switches,
http://www.ebay.com/itm/2Pcs-Thermostat-Temperature-Control-Thermal-Switch-Normaly-Open-N-O-KSD301-100C-/161318243058 Many more varieties to pick from on ebay.
The NO version would be fine. The problem I thought of personally was the homemade inverter gate that would have to be used on the NC version the OP posted.
using my Nylan M2300U panel. homemade relay based panels are unlikely to get fried using this method. i wouldn’t try this with a real FACP… you might fry it.
Just make sure that your panel’s power supply has fuses, so that if you accidentally short the power supply, it won’t burn your house down.