1) Any decent device manufacturer should have a record of the serial number of every device they sell. Bonus points if you mailed in your name and address and s

1) Any decent device manufacturer should have a record of the serial number of every device they sell. Bonus points if you mailed in your name and address and serial number so you'd be eligible for the warranty. 2) The MAC often is the serial number for many ethernet devices. (Most routers are weird because they usually have at least two or three MAC addresses, but it works out so long as you're consistent about which one you use.)