Abstract: A separation alarm, comprising a mobile telecommunication device (1) and a tag (2); the mobile telecommunication device comprising: a receiver (10), which is able to receive signals transmitted by the tag (2); a range calculator (12), which is able to determine, from the signals received from the tag (2), the range of the tag (2) from the mobile telecommunication device (1) to generate a range signal, and compare the range to a predetermined range limit; and an alarm device (4, 6), arranged to emit an alarm on instruction by the range calculator (12); the tag (2) comprising a transmitter (7) arranged to transmit signals to the mobile telecommunication device (1); in which the range calculator (12) is arranged to cause the alarm device (4, 6) to emit an alarm should the range indicated by the range signal exceed the range limit.