An alarm assembly is adapted for ease of assembly. A mortise cylinder has an exterior end and an interior end. The mortise cylinder has a tailpiece on the interior end and is rotatable about an axis. A cam engages the tailpiece on the mortise cylinder to provide selective movement of the cam responsive to rotation of the mortise cylinder. A housing secures the mortise cylinder and cam relative to one another and to a wall or door. A biasing member is disposed between the housing and cam for urging the cam into engagement with the tailpiece of the mortise cylinder, wherein variations in the length of the mortise cylinder can be accommodated.