Nice Kwikset! You could probably use a 12 volt DC power supply to power it to test it, then use a grill lighter a few inches below the sensor to provide a source of open flame to test it. It would probably be pretty sudden and loud though.
I was at a resort the other day and saw a gem. A BRK 79R. This was the first time I recall seeing one knowingly, and I recognized it right away. It had the 76RC’s round silver sensor, and I believe the newer single hole horn. It had its battery still connected. Here’s a pic.