Lidl are offering on Thursday a "Multi-Purpose Detector" which "Detects electricity up to 50mm, metal up to 30mm, wood up to 19mm, and cavities up to 38mm deep". I stumbled over wood until I realised they mean using it as a stud detector. But how pl. does it detect cavities?
PS I did look for the manual but it couldn't find one for the model shown in the photos.