My doorbell chime unit uses a DIODE to develop DC voltage for the longer front door chime sequence. Because an LED is also a diode, care must be taken to reverse the direction of the LED vs. the chime diode. The best way to do this is to try the bell before screwing down the button!!
The button is a good looking unit, and the light emitted is a pleasing golden glow (not a bluish LED look). I look forward to NEVER AGAIN changing a door bell bulb!!