Does anyone know of any wesites that show what an electronic bug looks like? (phone, computer, car)?

I am talking of course of electronic bugs that transmit audio surveillance. What do they look like typically? How can you find them if they are placed in something you own or where you live? If someone's car is bugged where would you look to see where the bug is located? Would the bug be connected to the car battery or would it be independent of any wiring from the car's electronic interface itself? Without expensive equipment how would I find these devices?