Can someone please tell me if there is a way of testing someone for drugs without them knowing it? Thank you

Yes, Hairs can be collected from the scalp of a persons head while their sleeping and a Hair drug test kit can be used to mail out the hair for testing.
This can give a 90 day drug history report for any unsuspecting individual.

Local pharmacies sell these test kits and/or can order them for in store pick up. They can be purchased online as well.