Geomapper module

Fallout 3
The Geomapper Module is a special item that can be received from Reilly after completing, Reilly's Rangers (quest)The device tracks data about any Primary Locations you find from your Pip-Boy 3000 and can be offloaded by Reilly at the Ranger Compound. She will pay 20 Caps per location found. It will also count the locations you have already discovered before receiving it. This item can be replaced by Reilly if you drop or sell it.

Note

 * cannot be replaced in 360 version
 * looks like the Stealth Boy