Many modern mobile communication devices are equipped with a global positioning systems (GPS) receiver and a navigation tool. These devices are useful when a user seeks to reach a specified destination as soon as possible, but may not be so when he/she only needs to arrive at the destination in time and wants to focus on some activities on the way. To deal with this latter situation, a method and device called “Space Time Alarm” is presented for helping the user reach the destination by a specified deadline. It does so by continuously and efficiently computing how much more time the user may stay at his/her current location without failing to reach the destination by the deadline. Advantage of this approach is that it works completely in the background so that the user’s en route activities will not be interfered with.