That's easy. Buy a DS700 security system from
x-10 and a wall thermostat. The thermostat
should be the kind with the tilting mercury
switch in the glass tube. Honeywell made them
and they were round. Hook the thermostat to a
door/window unit from the security package
and you're all set. Set the thermostat for
the temperature and you'll get a phone call
when that chilly temperature is reached.