Hidden device detectors? What to buy?

My father is obsessed with control. There are 20-30 visible cameras in\out of the house. And I've found several hidden ones over the years.
I found one again, and I'm done being passive. I also know he's been known to use tracking tags inappropriately.
He's cheap, and likely doesn't have any special spy surveillance devices...
I've used phone apps, which hint at things, but are limited.

I'm looking to purchase some entry level equipment to scan and find other devices. …

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