Methods and associated apparatus and programs for computers for operating geolocation devices are provided. The methods include determining the duration of a time interval during which the device is configured to remain active, responsive to a comparison between an estimate of benefit of remaining on for that time interval and an estimate of cost of remaining on for that time interval. The estimates of cost and benefit may be determined in response to user-selected parameters where by the end-user may effect a trade-off between battery life and receiver sensitivity. The methods also include varying the maximum duration of each listening period whereby to conserve battery power.