Not a big deal to open it up and check.
1. Push the little button on the back of the keyfob and slide out the key.
2. If you see a little plus symbol or no symbol at all, you have the older style keyfob.
3. If you see a round circle with a smaller round circle inside you have the new one.

http://www.therealmac.net/altima/200...ligent_Key.pdf