Do you want to make a prank on someone? How about hiding an annoying sound gadget somewhere? You should hide it during daylight, and when it will get dark, the sound gadget is going to simulate the sound of dripping water or a barking dog. If a person decides to switch on the light to find the source of the sound, then the gadget is going to switch off itself. The idea behind the gadget is brilliant, as it will be very hard to actually detect the source of the sound. If you got interested, then I can tell you that this device costs approximately $10, so it will not be a big investment. Have fun!