to test the heat detectors in my buildings
Is a gas torch an option?
These devices need a lot of current though. But perhaps you can carry a backpack with a large battery.
Is this an informal test, or are you doing some sort of certification/safety test? For the latter you need to know what standard you are testing against in order to know how to test it, and your test equipment would need to be calibrated.
I know all about it.