Does your campaign work on Hollywood guard logic? If so, then one character is indeed capable of taking out a guard patrol without raising the alarm. Does your campaign work on real world guard logic? If so, then you should be able to remain hidden as a stealth dedicated character, assuming you are optimized to the level of the campaign. This involves either a high stealth check, magical defenses, not going and scrying instead, a summoned creature with better stealth than you (either from unobtrusiveness or actual stealth), there's lots of ways. Remember: not every campaign is the same, and in fact, most are at a level where stealth works really well. I'm going to reiterate this:
A trap is something that performs at a level below the accepted power of the campaign it's designed for. Something that works less well than something else does not qualify as a trap. It takes the campaign into account before it qualifies as a trap. So: spell that functions well at a specific campaign power level that it was designed for: not a trap, even if there's a more powerful spell of the same level that does the same thing but better.
