BlackBerry smartphone users who own RIM or third-party holsters/cases/pockets/etc. with compatible sleeper magnets can also use those cases to lock their handhelds upon entry.

To modify your BlackBerry's holster-lock settings, open your main BlackBerry Options menu--the icon looks like a wrench in most BlackBerry "themes." Next, scroll down to the Security options and then open up the Password section. On the following page, fill in the checkbox next to the words "Lock Handheld Upon Holstering.

Finally, click your BlackBerry Menu key again and save your settings. (Note: If you use a password to lock your device, you'll need to enter it to modify this particular setting.)

Now your BlackBerry will lock anytime you place it in your holster/case/etc.