IPA: //ˈpaɪroʊˌstæt//
KK: /ˈpaɪrəˌstæt/
A device that controls temperature at high levels and can trigger alarms or extinguishers when it detects fire.
The pyrostat activated the fire alarm when the temperature rose too high.
Pyrostat → It is formed from "pyro-" (from Greek "pur", meaning fire) and "-stat" (from Greek "statos", meaning standing or stationary). The word "pyrostat" refers to a device that stands or remains in place to control or regulate temperature related to fire.
Think of 'fire' ('pyro-') and something that 'stands' or regulates ('-stat') — that's why a pyrostat is a device that controls temperature related to fire.