C.A.P. HLC-1 Heating Thermostat and High Temperature Shutdown 

The HLC-1 allows you to control the temperature within your growing environment. It can also be usedr as a high temperature shutdown to protect your garden. 

Just connect your heating equipment, then set the temperature that you wish to maintain. If the temperature falls below your setting, the outlet on the front is activated.

The C.A.P. HLC-1 can also be used as a high temperature shutdown by plugging your lights into the outlet and setting the maximum temperature that your growing environment can sustain. If this setting is exceeded, your lights will turn off.

Cheap insurance for your garden.

Comes with a 3 foot remote sensor. The HLC-1 is rated for 15 amps @ 120 volts.

More info from the Manufacturer (PDF format - Lots of detail.)