There are about a hundread differnet products you can buy for this at any electronics place. You can get probe thermostats, thermal switches, thermal transistors and a bunch of other temperature sensing devices that either open or close for rising or falling temp. Some reset automatically and some don't the ones that do are preferable. All come in either factory preset temps ranging from -10c to 300c from anywhere form 1.50 to up to twenty dollars. A friend has a 60c thermal transistor inline to his hotplate power source submersed in the oil bath for distilling sassy cost him two bucks and some wire crimps so he can interchange it with differnet ones when he is to distill iso or freebase. You can go all out and spent twenty bucks on a marked knob adjustable type probe that has a wide and very acurate temp range. But is unnessecary. The two dollar deal from EPO in houston made for microwaves works just fine and allows SWIM to travel while his reactions run them selves. Along with some infrared detectors and a few x/10 switches you can set up your reaction to start and stop itself while your gone to work.
edit-- Actually I just looked at their site again and they offer -40=400c ranges in all types and all sorts of devices.
