A security device

A security device comprising:

• a cellular modem for establishing a communications channel between the device and a base station of a cellular network;
• and
• a sensor for detecting an event within a monitored environment;
• wherein the device is operable in a first mode in which there is a first maximum interval between successive times at which the modem is able to receive cellular communications from the cellular network;
• wherein in response to satisfaction of a condition, the device operates in a second mode in which the modem is continuously able to receive cellular communications from the cellular network or in which there is a second maximum interval between successive times at which the modem is able to receive cellular communications from the cellular network, wherein the second maximum time is shorter than the first maximum time interval, and the device remains in second mode for a waiting period to enable receipt of an operator command via the cellular modem,
• wherein the condition comprises that an operator requested arming state for the device that is stored on the device when the event is detected by the sensor is an armed state.