Is it possible to connect 2 motion detectors on a light circuit so it will sense movement coming from either direction?? Answered

I'm new at this, so sorry if I need to add my question elsewhere. Armadillos are ruining my backyard and I need a way to notify me when they (or other critters) are in my backyard. I'd place some kind of sensor at each corner of my upstairs deck, with an alerting device in my bedroom. Stringing wire is expected to be needed. Max distance from the mounting points to the edge of the yard is about 50 feet. What do I need to buy to string this together?

What if you have a backfed light fixture, with two manual stitches branching off to either side of the room? Is it possible to somehow replace both switches with motion sensors in that case?

Just install the sensors back to back. It'll work.

Maybe this is easier to visualize.

88 percent probability of success assuming that the power from each detector is in phase.

Highest likelyhood of a problem is if you've got power from 2 different circuits, and those 2 circuits are 180 degrees out of phase. That. Could. Be. Bad.

That only works if the motion detector is capable of being bridged by a light switch.
Most simply give the mains voltage out on the white line but have no protection for anything comin in this way.
If they use a relay that simply switches the mains voltage to the white line you have no problem.
Otherwise I recommend using a relay on each motion detector.
Problem either way is that the light is activated twice, so you might want to use quite low timing settings.

Another approach could go like this:
Get a timer relay that won's restart the timer with a new signal.
Some offer a switch for that function but the most basic ones don't.
A good alternative can be these timers used for the lights in staircases of the old kind.
They always did what noone wnated: No matter what you tried the lights had to go off before you could turn them back on.
Hard to find these days but sometime you get lucky at a garage sale.
With the motion detectors set to the lowest timing or testing setting you can now use their relay output to start the timer relay.
Great thing is that the light always stays on for the same amount of time, bad thing is that with a lot of traffic it might go off when you don't want it off.

I would wire the two motion detectors as below and added an override switch.

Be sure to click the pic to see the whole image...

Can't say with certainty without seeing the insides of the units, but it sounds plausible.