A few weeks ago, my brand new $300 cell phone was stolen in a restaurant. Even if the police cared about this kind of thing (hint: they don't, despite that cell phones routinely cost more than bicycles and can contain more confidential information than your tax returns and are increasingly used as personal computers, not phones), it would be hard to prove anything without a serial number, and I didn't have mine.

So I started a spreadsheet inventory of everything I own, including the following points of detail:

item
serial number
model number
date of purchase
retailer (and customer service phone no.)
warranty information (length and approximate terms)
purchase price
estimated present-day value
memo

There are several uses for this information.

Law enforcement will be able to identify property that has been stolen from you.
You will be able to prove losses to your insurance company in the event of burglary or destruction of goods.
If an item needs to be returned, repaired, or replaced, you have all the phone numbers in one place. You don't need to dig through a box to find the manual and customer service line for a particular item. And when you do call the company for service, the representative won't need to wait for you to fumble around with the device trying to find the number on the back of your computer, or trying to determine what model you own.
If you're about to go bankrupt, you can sort the sheet by "estimated value", greatest to least, and sell whatever you need least, starting at the top.

Under "memo" I noted other identifying details, such country of origin, and so on. In that area, I recorded MAC addresses (a unique identifier) for computer networking devices such as laptops, wireless routers, and network cards. That way, if the thief logs onto the wireless at Starbucks or a nearby university before selling my laptop on eBay, an administrator can check the router's logs, making it easier to track down where it went after I lost it.

As may be expected, I skimped on nothing. In fact, for items with multiple components, like computers, I wrote down serial numbers for each major component in the device (hard drives, memory, etc.) It may be overkill, but I won't be complaining about the time I wasted on this spreadsheet when a detective links a suspect to my case based on the serial number for my one square inch digital camera memory card after the thief has "parted out" my equipment.

There are several reasons why doing so earlier is better than doing so later.

You will save an enormous amount of time and frustration if one of the above events happens to you. If the police or insurance company asks you what was stolen, you click "Print" and circle anything you can't find in your house or car.
You will avoid arguments and resentment with roommates over ownership disputes.
You'll have less items to catalog now than later.
It's a fun activity, especially if you're obsessive-compulsive or paranoid.

In this post I have ignored an obvious and admittedly more serious threat specifically associated with electronic devices ? identity theft. I still need to secure the contents of my data with encryption, back them up efficiently and regularly, and perhaps implement a software or hardware anti-theft solution.