Thanks a lot for the quick response. I guess, I better keep coordinates and "offset" separated... ;o) Best regards, T.

The price of LIDAR units has gone down significantly - https://www.robotshop.com/uk/y... - you could mount one of these above the wall and detect people reaching out - not reliably down to fingers at a distance, but would expect to hand or arm size - could do some tests and post the results if you are in interested.

@skulpture Thanks very much!