It would depend on the type of bug /camera and how they are wired.
A long term bug/camera would be wired into the mains for power, so an electrician maybe able to find it.
Depending on the way that the bug/camera could be picked up would depend on how the transmission is sent a spectrum analyser would probably see wireless ones, but some listening devices can be very covert using short bursts of data and even detecting sweeping devices.
There are some professional sweepers that look for transistor junctions/ diodes etc.
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