NuTone LA201 Door Buzzer, 3-Volt to 6-Volt DC Door buzzer uses transformer or 3 to 6-Volt DC voltage 2 1/2-Inch wide x 2 15/16-Inch high X 1 1/16-Inch deep From NuTone, the creator of the first door chimes and still recognized industry leader Model number LA201 Extensive line of door chimes also available