A method performed in an access control system for determining whether or not to arrange to carry out an action in response to an event generated in the access control system, wherein the access control system comprises a control unit connected to multiple mobile devices using radio-frequency signal communication, and further comprises a radio-frequency transceiver, and wherein the event indicates a request for the control unit to arrange to carry out the action, the method comprising: transmitting, by the radio-frequency transceiver, radio-frequency signals to be used for measurements of received signal strength by the multiple connected mobile devices; in response to the generated event, sending by the control unit, a motion status request to a respective connected mobile device out of the multiple connected mobile devices; determining, by the control unit or by the respective connected mobile device, an indication of a probability that the respective connected mobile device is associated with the event, wherein determining the indication of the probability is based on received signal strength data and motion sensor data of the respective connected mobile device, wherein the received signal strength data is measured by the respective connected mobile device and based on the radio-frequency signals transmitted during a first predetermined period of time before the motion status request from the control unit is received, wherein the motion sensor data is collected from a motion sensor, comprised in the respective connected mobile device, during a second predetermined period of time before the motion status request from the control unit is received, and wherein the motion status request functions as a trigger for the respective connected mobile device to compile received signal strength data and motion sensor data that is to be used for determining the indication of the probability that the respective connected mobile device is associated with the event; and determining, by the control unit, whether or not to arrange to carry out the action based on the indication of the probability that the respective connected mobile device is associated with the event. transmitting, by the radio-frequency transceiver, radio-frequency signals to be used for measurements of received signal strength by the multiple connected mobile devices; in response to the generated event, sending by the control unit, a motion status request to a respective connected mobile device out of the multiple connected mobile devices; determining, by the control unit or by the respective connected mobile device, an indication of a probability that the respective connected mobile device is associated with the event, wherein determining the indication of the probability is based on received signal strength data and motion sensor data of the respective connected mobile device, wherein the received signal strength data is measured by the respective connected mobile device and based on the radio-frequency signals transmitted during a first predetermined period of time before the motion status request from the control unit is received, wherein the motion sensor data is collected from a motion sensor, comprised in the respective connected mobile device, during a second predetermined period of time before the motion status request from the control unit is received, and wherein the motion status request functions as a trigger for the respective connected mobile device to compile received signal strength data and motion sensor data that is to be used for determining the indication of the probability that the respective connected mobile device is associated with the event; and determining, by the control unit, whether or not to arrange to carry out the action based on the indication of the probability that the respective connected mobile device is associated with the event.