A look inside an inexpensive Sound Activated Touchlight. This product was purchased from Princess Auto in the surplus section. There are just a handful of components that makes it work since this was probably a 4 or 5 dollar product when it was in a regular retail store. I purchased it for about a dollar. In touch mode the push dome simply presses a push on/push off button. In the sound mode it takes the output of the microphone which is AC coupled to a single transistor amplifier. This mic signal charges a large electrolytic capacitor which slowly discharges, while it is greater than 1.1 volts the lamp lights. A photocell prevents the automatic sound operation from operating when there is sufficient ambient light. I was surprised to see a lamp in this thing but I guess it could be 10 years old when lamps were still common in battery operated lights. The current draw is quite significant when lighting at more than 1/2 and amp at 6 volts. To bring things a bit more up to date a few under driven 1 watt LEDs were installed to allow this device to operate for much longer than it would with the light bulb.