Dungeons and Dragons

As a GM I could work around the familiar exploring. What's the range of control? What's it's passive perception, or stealth? What's the CR of perception checks for traps, or stealth rolls for enemies? Does the familiar have dark vision? Is it heavy or tall enough to trigger a trap?

As long as i know the abilities of the PCs, including familiars, I can balance the encounter. That's part of the job, really. Make sure the encounter is balanced and fun* for the players.

Even if the familiar's perception is high enough to find traps, that's not an issue if you use the PC's greatest enemy: doors. "As Mister Snugglebutt turns the corner they see a closed door barring their path. (On a successful perception check) A few feet up the path there is a small fissure. It leads to a narrow passage that winds down further into the caverns. A light appears at the end of the passage, and the sound of movement can be heard in the distance. As Mr Snugglebutt approaches…what was the range on control again? (Meanwhile behind the door is a trap laden corridor that the familiar bypassed entirely, but the party must use)

tl;dr: give me a familiar and I'll give you The Adventure of the Alerted Guards: How My Cat Just Turned This Into a Prison Break Story.

*for a given value of fun