There’s a bird that does that outside my window and last spring was the first time I ever heard it but it’s exactly like you said - three short chirps then silence for a minute. I also thought an alarm was going off but it sounded like a low battery warning sound inside my house. The birds outside my window chirp for hours at a time, how long have you been hearing it? Fwiw, the Merlin bird ID app said it was an Ash-throated Fly Catcher.