These AP65 heat detectors are for use with Fireboy-Xintex FR Series Fire Detection Panels, and are designed to alert you when a "pre-fire" (high temperature) situation exists, so you can correct it before your installed fixed fire extinguisher system is set off.
The fixed fire extinguisher system goes off at the factory pre-set 175F, but the detector alarms a little earlier at 170F.

This AP65 heat detector is a "non-addressable" detector, for use with non-addressable fire detection panels which are designed for use in recreational vessels, which typically have a smaller number of detectors installed.
All the multi-zone FR series of fire detection panels that well sell fall into this group)
An alarm from one of these non-addressable detectors will show on the panel as coming from a particular zone (say, your engine room).
An addressable detector, on the other hand, must be used with an address-capable panel, but will provide the exact location of the "alarming" detector on the panel's display. This is useful when the vessel is large enough to have many detectors (e.g. 150) - typical on a large ship - and knowing it is in the engine room just isn't enough information.

Hardwired (user supplied wire)
Supply voltage: 10 - 30V DC, for use with 12 or 24 volt systems (auto sensing)
UL listed