Finding hidden cameras
For finding a wireless camera, people have long used "bug detectors" to hunt for unwanted RF transmitters and other electronic devices that unintentionally emit RF. There is no reason they wouldn't find an actively broadcasting Wi-Fi device.
For a wired device, use a tone generator and detector (often called a fox and hound.) Clip the fox to the first wire plugged into a switch, and start tracing it with the hound. Once you've found its terminus, move to the next wire.
A physical problem requires a physical solution.
Interesting question. Theoretically a sophisticated attacker could place hidden cameras that can't be detected, but theoretically a competent defender has logs about everything to catch attackers trying to deploy any unwanted stuff.
So in this case this boils down to how sophisticated an attacker Mallory is (as it's proven that Bob isn't a competent defender).
Threat Analysis:
Bob should start by conducting a simple background check against Mallory.
Main questions that should be answered: Does she have technical background? (More specifically: Does she have the necessary knowledge to set up something like this?)
Does she have the necessary resources? (Hiring someone else to set something like this up isn't cheap. At all.)
What difficulties might have been encountered by Mallory while setting this up? (Answers to this question could also be used to look for proof about the cameras existence.)
Did she have the opportunity to set this up? (And are there "logs" {security camera tapes, bills, etc.} from this time that could indicate the "attack"?)
Anything else based on data already know about Mallory, and might be applicable here.
Answers to these questions might indicate if the claim is true or not, and they could also give hints about the cameras whereabouts.
Some things I'd check:
Electricity:
Cameras (and the equipment to control them) need electricity. This can be supplied by batteries for a short time, but for extended operation they need to access the grid somehow. I'd check how the electricity consumption per day of the house changes now that Mallory isn't there and compare it to other days when she was there (and when she wasn't but hadn't probably deployed the cameras yet) and look for discrepancies.
(Also checking for additional power cables that weren't there before might be a good idea.)
Command:
She is supposedly having remote access to the cameras. This can take two forms (when observed by Bob), inbound and outbound communications.
Assuming that the house has only a single connection that is capable of accessing public networks (as most homes do), it shouldn't be too hard to monitor it.
A good check could be to disconnect everything that belongs to Alice and Bob from the network and check if there's any suspicious communication going on.
(Though the cameras might use other means to access the public net.)
External help:
Getting external help isn't cheap so unless someone owns Mallory a big favor she would have had to spend quite a lot to get someone to help her. (Getting access to her financial data might conclusively disprove outside help.)
These checks can't conclusively disprove the cameras existence but might catch them if they do exist.
- Bob could sniff the traffic.
- Bob could search the house again.
- Bob could use lsof -i:49152 to check what program is running on this port if he can access the PC.
- Bob could ask Mallory if she's kidding because this is annoying