There are temperature sensors that will operate over a range of approximately -20 degrees C (-4 degees F) to +60 degrees C (140 degrees F). My garage is attached to the house, so it never exceeds that range. The trick would be to get the sensor to set off an alarm siren before the s sensor fails.
In a fire situation, especially if accelerants such as gasoline are involved as is often the case where cars, lawnmowers, gas cans, etc. may be stored, the temperature can increase so rapidly that the sensor may fail before an alarm is triggered.
Unless you have access to a fire tower where firefighters train, there would be no way to testing to insure your setup works as intended.