As the name implies, Plan B is a good option for people who haven&39't thought ahead and downloaded a lost-phone locator app on their Android phones before the phones go missing. This app lets you do it after the fact over the Web on the Android Market Web site.

Mobile-security company Lookout released a new free Android app today called Plan B that lets you find a lost phone without having downloaded special software onto it beforehand. You just install the app over the Web after the device goes missing.

To use the app you need access to the Android Market Web site and a Google account. Once the app is downloaded over the Web, an e-mail arrives in the associated Gmail account telling you the app is locating the phone, followed by another e-mail with a Google Map showing where the phone is.

Plan B will send follow-up e-mails for the next 10 minutes with updates on the whereabouts of the device. In order to locate the phone, Plan B sends a text via SMS and uses cell towers and GPS to locate the device, even if GPS is turned off.

If you aren't able to find the phone within the first 10 minutes, you can use a different phone to text the word "locate" to your missing phone to start the process over.

I downloaded the app and it was close to finding my phone's location, but it guessed that the phone was at a shop that's just around the corner from where the phone was located on my office desk. The final e-mail pinpointing the location (I received five of them) indicated it had located the device within 24 meters, or about 79 feet, which seems fairly accurate.

Plan B sends e-mails with Google Maps links showing updated locations for the lost phone.

The service is available only in the U.S. at this time on AT&T, Sprint, Verizon, and T-Mobile and only on Android 2.0. Plan B will not work if the phone is turned off, has no SIM card, or has no network connection. To test, call the phone and count the rings. If it rings once and goes right to voice mail, your phone is off.

The app, available here, is the first release from Lookout Labs, which was created "to explore and test out new ideas that push the boundaries of mobile," the company said.

More information is on the Lookout Blog.