Removing plywood from floor

[John D v2.0]

I thought you were taking the Mick.

I was wrong. Thanks.

https://www.cnet.com/how-to/how-to-turn-your-android-phone-into-a-metal-detector/

To be honest I didn't believe it at first, I was just googleing for metal detector devices in frustration, and some apps popped up, I assumed they were scam apps a bit like the ones to charge your battery without plugging in, but they looked legit and after installing one, it literally worked!
The only drawback was you couldn't tell where the active point was as it uses the compass detector, so I had to do it again with the phone 180 degrees rotated, put an X in forward and reverse direction, and drill between the 2 X's.

 

[blup]

A rare earth (neomydium) magnet is a quick and effective way of finding buried screw heads. But it's pulled into the metal at speed and will shatter if not held firmly.

Blup