This mod was so amazingly simple. A couple of weeks ago I saw this ad in some Harbor Freight flyer I got.
Since I had a coupon I decided to try one out. I am sure glad I did, now I am ready to pick up a couple more.
There are two parts, a motion sensor transmitter and a receiver chime.
I wasn’t going to modify the transmitter, I just worked on the receiver part.
It uses either 3 C Size batteries, there is a label outside saying it can take a 6 volt DC power supply as well, but I tried a 5V power supply and it works too.
There are 6 screws holding this shut, 4 slightly larger screws were external, 2 were under the battery.
I looked at the PC board and using a digital multimeter I was able to identify the where the chime signal came out.
When the alarm triggers, it sends a .4V signal down the signal line. Attaching the other link to your arduino, rasperry pi, or esp8266 ground makes this thing work.
In my arduino code I simply use the digitalRead function. I am decided to use a NodeMCU.
The actual hardware mod took less than an hour, now that I know what plugs where, I would say it would take me half an hour to do one.