I imagine Camry uses basically the same system as the Prius. As others mentioned, there is a mechanical key inside the fob, push a button and it will slide out. As I recall that mechanical key is intended for emergencies.
Also, as others also mentioned, your problem is almost certainly a dead or dying battery. Mine use the coin shaped battery (2032) which you can buy at almost any drugstore, big box store, etc. Search on youtube for your year and model and you almost certainly will find a couple of excellent videos on how to open the fob and replace the battery. It's not hard. Alternatively you could take your fob to a Toyota dealer who will gladly charge you $100 or so to do it.