Tohoros 7:2

If a learned person left an unlearned person in his house awake and he returned to find him awake, or if he left him asleep and returned to find him asleep, or if he left him awake and returned to find him asleep, the house remains clean. If he left him asleep and returned to find him awake, Rabbi Meir says that the house is unclean. The Sages say that only the part that the unlearned person can reach out and touch with his hand is unclean.

Tohoros 7:3

Rabbi Meir says that if a person left craftsmen in his house, the house is unclean. The Sages say that only the part they can reach out and touch with their hands is unclean.