Too bad you don't seem to be able to invert the "Effect Use" effect modification and have a device not work for a specific list of people.
One way to trap a lab would be to have common items that anyone entering the lab would expect to use become triggers- for example a lantern that has a spell to emit light if a code word is use also being enchanted to do something nasty if someone attempts to light it. A drawer in the desk which holds nothing but a curse on whoever opens it, or a doorknob which is fine if you turn counterclockwise but not clockwise...
False doors make fun traps. Looks like a real door, but try to open it and ZAP! Invisible doors or walls that have spells that go off if people try to walk through them.
Why not?
"Does not trigger when I touch it" is really the same as "Works for the specific list of people that is everyone but me."
I may be the discordant voice here, but spending seasons and seasons to create enchanted devices to trap a lab is definitely not something that my PCs (and thus the vast majority of my NPCs) do. In my saga lab "traps" take two forms:
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Intelligent guardians (familiars, summoned spirits, a grog with second sight on guard etc.) whose main purpose is to detect suspicious activity and raise the alarm with the magus, his sodales etc. or activate other defenses "manually".
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D:Ring effects. It's really surprising how much mileage one can get from clever use of low level (i.e. often spontaneous!) D:Ring effects. These tend to be effects of two types: those that present a constantly active "hazard" easily avoided (only) if you know about it, and those that block some hazard and thus release it as soon as the Ring is inadvertently broken -- again, something easily avoided (only) if you know about it.
Give me an Art breakup of the magus in question, and the location/layout of the lab, and I'll give you examples!
I wonder if there are any of Himnis' Curses that might exist specifically to trap labs. For example, a curse that inflicts the Delusion Flaw that makes the intruder think the lab is unlootable or that he is an enchanted guardian of the lab. Or one that inflicts the Indiscreet flaw on intruders, so that they can't help but confess their crime.
In general, you're absolutely correct. Traps in your lab make your lab more dangerous for YOU and everyone who might assist you, and suck away valuable seasons that (especially) young magi need for self-improvement. Older magi, for whom improvement is difficult and who often accumulate both valuables and enemies, might consider investing in such, and they generally have the arts to do so efficiently.
Also, if your sanctum has been breached once in the past, you'll start thinking about adding these defenses. Dysfunctional covenants will breed the kind of paranoia that makes magi add them. But for a functional, friendly covenant (most PC covenants), they really are not practical.
Ring spells are great but generally are pretty easy to detect. This makes them an excellent distraction, though. Even a mundane painted circle can suffice for this.
And saving seasons is another reason for mundane traps, again especially if you expect your enemies to be watching for magical ones...
One possibility, assuming you do not have any assistants, is to have a hazard which you simply survive by virtue of your art bonus. For example a terram mage can set up rock throwrs that pelt the person when they walk through the door or perform other standard actions. If the mage has a +8 soak bonus (40 terram) and wears heavy leather armor, or has stamina 2+ if the attack does +0 damage he could take stone peltings all day and not worry about it...
Hmm, I don't see why they'd be that much easier to detect than enchanted devices. It's not as if they even have to be visible.
A ring has to be drawn, it can only be traced if it is a pre-existing circle (band laid into the ground) so, yes, it does need to be visible.
My magi are going to start decorating with circles.- a floor engraved with interlocking circles can drive intruding magi mad...
Nested circles could be hidden magically, to create simple alarms. One ring makes a loud noise. A second ring outside it has two effects to hide both rings and stop the noise. When the first is broken (because it's drawn in flour or salt) by a foot or door opening the noise starts.
An active spell is easily detected and analyzed (at least for Te/Fo), but an enchanted device generally only registers as vis (and a charged item won't register as vis at all) and can't be analyzed without a season of work.
And concealing a Ring with other magic just means more seasons of work (PeVi and MuIm spells?)
What if you had a somewhat obvious active circle "trap" that you just ignored because it doesn't really do anything, but an intruder would analyse, while the real trap is set to target the caster of the analysis spell?
Or a mechanical trap with a timing mechanism so if you stood too long without walking across the circle...
Of course a circle could also be used to simply contain a magical entity which is invisible and bound not to attack the magus or those he designates as trusted...