I happened to be near an Aldi supermarket the other day so i had to have a look at the tools area.
They had a stud finder for £10 so I thought I'd take a chance.
https://www.aldi.co.uk/en/specialbuys/s ... etector-2/
On first testing I thought it was as useless as I'd expected it to be but as a last resort I read the instructions.
it looks like you should hold it square to the wall and point the round end to do the finding... but you don't. You hold the whole thing against the wall and slide it sideways to detect.
Using it like that is successfully found metal through plasterboard and found timber battens as well. The live wire function worked well also.
So if you need one its not bad for £10