Nano first generation you can trade it in for a free replacement. Apparently the batteries on the 1st generation may overheat so there letting everyone who has one get a replacement.
Here is a link
http://www.apple.com/support/ipodnano_replacement/?cid=CDM-US-DM-P0010121-CON&cp=em--&sr=em
So if you have one might wanna trade it in.
Inb4 cool story bro