A method for determining a distance between persons, comprising: providing a plurality of devices (1, 1', 1"), each associated with a person and each comprising a battery, ultra-wideband, UWB, tag and UWB anchor, the UWB tag and the UWB anchor being energized by the battery and the UWB anchor being substantially disabled; wherein each of the plurality of devices (1, 1', 1") is configured to periodically or quasiperiodically repeat a typical operating pattern; the typical operating pattern comprising the steps of: - enabling the UWB anchor during an announcing period ; - transmitting an announcing signal of the UWB tag comprising an indication of a transmission time; and - transmitting a ranging signal at the transmission time; wherein, when an announcing signal from a first device is received on a second device (1") during an announcing period of this second device (1"), the second device (1") initiates an atypical operation pattern; the atypical operating pattern, comprising the steps of: - determining an anchor wake-up period for the second device based on the transmission time of the received announcing signal ; - enabling the UWB anchor of the second device (1") during the determined anchor wake-up period ; and wherein the atypical operating pattern is configured for - receiving the ranging signal on the second device (1") during the determined anchor wake-up period ; wherein a distance between the first device and the second device (1") is determined based on the ranging signal from the first device , which is received on the second device (1"). providing a plurality of devices (1, 1', 1"), each associated with a person and each comprising a battery, ultra-wideband, UWB, tag and UWB anchor, the UWB tag and the UWB anchor being energized by the battery and the UWB anchor being substantially disabled; wherein each of the plurality of devices (1, 1', 1") is configured to periodically or quasiperiodically repeat a typical operating pattern; the typical operating pattern comprising the steps of: - enabling the UWB anchor during an announcing period ; - transmitting an announcing signal of the UWB tag comprising an indication of a transmission time; and - transmitting a ranging signal at the transmission time; - enabling the UWB anchor during an announcing period ; - transmitting an announcing signal of the UWB tag comprising an indication of a transmission time; and - transmitting a ranging signal at the transmission time; wherein, when an announcing signal from a first device is received on a second device (1") during an announcing period of this second device (1"), the second device (1") initiates an atypical operation pattern; the atypical operating pattern, comprising the steps of: - determining an anchor wake-up period for the second device based on the transmission time of the received announcing signal ; - enabling the UWB anchor of the second device (1") during the determined anchor wake-up period ; and - determining an anchor wake-up period for the second device based on the transmission time of the received announcing signal ; - enabling the UWB anchor of the second device (1") during the determined anchor wake-up period ; and wherein the atypical operating pattern is configured for - receiving the ranging signal on the second device (1") during the determined anchor wake-up period ; - receiving the ranging signal on the second device (1") during the determined anchor wake-up period ; wherein a distance between the first device and the second device (1") is determined based on the ranging signal from the first device , which is received on the second device (1"). <EOS>