They are part of an alarm panel that Aqua Signal provided to me (for the three bilges and engine and generator). They work fine except that the generator has an intake hose that doesn't generate enough flow through the engine -- therefore I get occasional transient "alarms" when the generator is running at very low load. I have a reset switch the mutes the alarm -- then if I loose an impeller, it goes off like crazy. However it works very well on the engine. (i.e., it almost NEVER goes off :^) -- except if the seacock is closed for some reason or I get a blockage from ell grass or something.)