I retired a motion sensing light because water got in the motion sensor pod and it stopped sensing motion like it's supposed to. Now I'm taking it apart. This post focuses on the motion-sensing sensor section.

I cleaned everything before the teardown, so sun damaged caused the discoloration visible here. We can really see where this sensor pod was shaded by adjacent light pods and where it gets hit with sunlight. The mounting thread is pristine, as it was safely shaded by the sheet metal base.

A single screw holds the elbow joint together and is easily removed for disassembly.

The wrist joint is a different story. I see no visible fasteners and, to make things more complicated, it blocks one of two screws holding the sensor pod together. I'll look at other parts of the sensor pod and come back to this headache later.

There are two adjustment knobs on the bottom of the sensor pod. Looking through the damaged sensor window, I can see they're connected to rusty potentiometers inside. No fasteners or retention mechanism visible from here, so I'll try giving it a hard yank.

Brute force pulls them out after overcoming a retention clip mechanism I couldn't see before. There's also a small soft translucent rubber band to mitigate water intrusion.

One of the sensor pod screws came out easily, but the other one is still blocked by the wrist joint I couldn't open. I have no good ideas on how to access that screw, but looking inside the sensor window I could see where the screw threads into. I could use my Wondercutter to cut that off at the base. It should be able to cut this plastic but it can't cut metal, so I referenced the removed screw length to know where to cut in order to avoid the still-installed screw.

Once cut, the pod opened to reveal far more electronics than I had expected. I thought this was one of those products where component count is squeezed to an absolute minimum. So I expected to see a single circuit board with a half dozen components. There are actually two boards separated by a piece of clear plastic, connected by a 4-wire cable, and I estimate several dozen components across both boards.

Two rusty screws held the front board in place, two more held the rear board in place, before everything came apart.

Now that I can look at the wrist joint from the inside, I can see there was no elegant way to remove it. I would either have to pull on it hard enough to overcome these one-way clips, or cut something. I guess I had accidentally stumbled into the least-cutting way to open this sensor pod.

The inside of the sensor window showed a series of ridges characteristic of a Fresnel lens, a feature I didn't notice until I could see these pieces from their back.

I had hoped to find a simple circuit board I could understand. The unexpected complexity meant it was beyond my current skill level to decipher how everything worked, but I could still give it a try to see how much I could pick up.