The present disclosure relates to a method and devices for transit-time-based distance measurement and the teachings may be applied to locating keys for a motor vehicle. In one embodiment, a system for detecting the distance between a vehicle and an associated key may include: a transceiver associated with a vehicle; a key for the motor vehicle; and a processor configured to determine an estimated signal transit time between the transceiver and the key based at least in part on a ratio of a length of two time intervals between the transmission or reception of a message between the transceiver and the key.