Link (Thanks, Bonnie!)
In simple terms, the Sputnik satellite was a metal sphere almost 2ft (61cm) in diameter, containing a radio transmitter. It also had a battery; equipment to measure temperature; barometric and temperature activated switches; and a fan to stop it getting too hot.
It sent its famous "beep beep" radio signals to earth, altering the transmission to indicate changes in temperature or a sudden drop in pressure caused by a puncture in the satellite's case. And that's about it.
You could probably find most of these components lying around your home. There are transmitters in mobile or cordless phones, wireless internet routers and baby monitors, and you may well have a thermometer in the medicine cabinet.
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.