It’s literally a device designed to do exactly what I sometimes need (start an action if a circuit closes) and I just never thought about it even though I know how leak sensors work and that there are ones available. Duh!
Stuff like that is why I love HN. Thanks to the author if you’re reading.
I guess that would also be a really easy to do the opposite (if it mattered) since a reed switch triggers the action when it opens, but a leak detector when it closes. Or I guess maybe they do both.
I am curious why the leak detector is bigger if it’s a simpler device. Basically the same thing but without the reed switch right? Maybe just to make room for more battery since you actually care how big the door sensor is.
I think a leak sensor is more complicated because it needs to detect a somewhat lowered resistance between the contacts, as opposed to the door sensors that will get a fully closed/opened reed switch on activation. Detecting lower resistance with some threshold in a battery powered device that needs to sleep most of the time is probably more complicated. I would guess waking up on a pin state change is built into most microcontrollers, while measuring resistance to make it wake up requires additional components?
The door sensors on my alarm do make it many different noises on open/close so that one must trigger on both. How cool.