Lock and unlock your computer with a USB drive, secret-agent style

 With Predator, you can turn your USB drive into a "key" that unlocks your computer when plugged in, and locks it when it's removed.
if you prevent access to your computer with just a password, you are missing out on an alternate (and more secure) way to lock down your computer.
Predator, a free Windows program, turns your USB drive into a key that locks your computer when it's removed. To unlock your computer, you'll have to plug the USB drive back in. (Talk about having secret-agent-style security.)
Anyone who attempts to access your computer without the USB flash drive will be hit with an epic "Access Denied" message. To get started, follow this guide:
Step 1: Download and install Predator.
Step 2: Once Predator launches, plug in your USB flash drive. None of the contents of the drive will be deleted or altered in any way, so feel free to use your primary thumbdrive.
When you insert the drive, a dialog box will appear asking you to create a password. Click OK to continue.

Step 3: In the Preferences window, take note of a few key settings. First, enter a secure, unique password in the "New password" field. If you lose your USB drive, you'll use it to unlock your computer.
If you'd like, you can check the Always Required box and you'll be asked to enter the password each time you use your thumbdrive to unlock your PC.
Finally, in the section under Flash Drives, ensure that the correct USB flash drive is selected. When you're done, click "Create key" and then OK.

Predator

Step 4: Predator will exit. When it does, click the Predator icon in the taskbar to restart the program. A few seconds later, the icon will turn green, alerting you that Predator is running.
Every 30 seconds, Predator will check to see that your USB drive is plugged in. If it isn't, your computer will dim and lock down.
Here are some extra tips:

• To pause Predator at any time select "Pause monitoring" from the taskbar menu.
• If someone tried to access your PC while it was locked down, you'll see the activity log when you log back in. You can see the log at any time by clicking "View log" from the taskbar menu.
• Predator's Web site has several cool how-tos, including one that shows you how to program your computer to take a snapshot each time someone tries and fails to log in to your computer. Check it out.

One obvious flaw comes with this setup: you'll always be down one USB port. But if you're sold on Predator, consider purchasing a USB hub to compensate.