If Perception only then at a higher Difficulty unless they have the Tools for the Job (some kind of bug sniffer).

Yes this makes sense to me. Just looking for a bug with your eyeballs, Perception. Picking up a scanner use Computer and remove a difficulty die, it's a completely different (and easier) task.

I'd probably default to a Perception roll, unless the players suggested a different skill. There are many ways to go about looking, like others have already pointed out. One's innate knowledge of bug-planting could be more useful than another's general awareness, since knowing where to look is often much better than simply looking.

Also, don't forget "Spend [Advantage] to notice something important." Noticing a bug could be an auxiliary result of performing nearly any other task, with some creative narration.

Our GM adjusts the difficulty of dice pools based off of what skill you use.

Example (don't quote pools, its just an example)

We noticed that our ship had been tampered with and there was evidence of somebody being onboard. When looking for anything out of place we rolled Perception (RPPP). When people went to specific parts of the ship to look for things, they ended up using the skill applicable to the station. Mechanics in engineering (PPP), Pilot in the cockpit (PPP) and so on. Computers with somebody walking around with a scanner looking for odd signals had the lowest difficulty (PP) when he stated he was looking for a tracking device.

Player: "I search for bugs."

GM: "Use [skill]."

Player: (Success) "Found one!"

Group: "What!?" "Dammit!"

GM: "Speaking with hotel management, you discover every room has been bugged at one time or another. Various reasons and entities involved. It's too time-intensive for the staff to do thorough searches, so it is what it is. There may be no way to determine if this is specifically related to your current endeavor or just a leftover from some previous skullduggery."

Dun dun dun...!

"Of coures there are bugs in our establishment... This is Bothawui, what did you expect?"

Is a phrase that will be spoken at our table quite soon.

Going with the bothawui example, would every success net a found bug?

I've honestly been very impressed with how many skills are useful in this game.

We use Athletics, Discipline, Perception, Pilot (both), Vigilance, Cool, Mechanics, Computers, Knowledge (mostly Education, but the others as well), and Combat (any) all on a regular basis. Some characters use Stealth and Skullduggery fairly often as well.

It's pretty cool. I like that it gives all the players a chance to be awesome as long as you try not to step on each others' toes too much.

For searching for surveillance equipment I'd use in order:

Skullduggery

Stealth

Computers

Perception

Knowledge Underworld

Mechanics

Actually, with bugs of a certain size I would suggest that the tool (scanner) may be required to accomplish the task (perception check). It is similar to how they do scanners on star ships.

Of course if the bugs are large enough then ymmv on a straight perception check.

I would say Perception if you are actively looking for listening devices in a given area. Vigilance is more of an 'oversight' skill, to me. You are paying attention to everything and nothing.