@sunnyboy69 Getting false readings can be anything as it depends if it is a serial read from the device or simple timing of the echo, unstable voltage, or even an object caught in the path of quite a wide cone, but without further details it is impossible to identify. I've been caught before with a serial reading device, took a while before I realised.... An extension of what @bjacobse suggested is to repeat readings until you get two identical consecutive results which are <> known limits and not cuckoo results..