Last year, I bought a JP-200W just like this one here on eBay, but it was in worse condition than I planned. I kept it anyways and kept a lookout for one that was affordable, but in better condition. 

I bought this one as "untested. needs a battery". Well, it needed a battery, sure. After getting the back off, the built-in module clip to keep the battery bar clamped down was broken and I had to improvise to get it to work. 

Once I got the case back on, the sensor didn't work. 

Looks like I'm keeping the first one I have. Maybe someone can fiddle with this one and get it to work. I'm only asking $15. Buy it today.