Question: Do police have to be within their jurisdiction to pull me over for DUI in Maryland?
Answer: Yes, actually, the police officer who stops you has to be a licensed police officer in that jurisdiction. So, a Washington County officer cannot pull somebody over in Baltimore County—unless the officer saw the conduct happening in their own county and followed the defendant into another county. So, if a Howard County police officer sees a car swerving and then it goes into Anne Arundel County, the officer may pursue an arrest based off of the driving, erratic driving that he saw in his own jurisdiction.
But, if a out–of-county officer or out-of-city officer observes everything happening in the jurisdiction with which he is not licensed in, then it is a valid defense to a case that the officer had no jurisdiction to pull a defendant over.