buzz up

To remotely and electronically unlock a door on the ground level to allow someone to come up to a higher level of the building (an act often accompanied by an audible buzzing sound). In this usage, a noun or pronoun can be used between "buzz" and "up." Text me once you get to my apartment building, and I'll buzz you up. Tom, will you go buzz up the courier, please? A: "Why are you standing out here in the cold?" B: "Well, I rang the bell, but no one will buzz me up!"