A system comprising a plurality of devices configured for use at a site and a remote computing system that is not located at the site, the plurality of devices comprising: one or more sensing devices; and one or more other devices for performing an action commanded by the remote computing system; wherein each of the plurality of devices is configured to periodically send a proof-of-alive signal to the remote computing system on a wide area network, WAN, the proof of alive signal comprising a WAN address of the remote computing system and/or an identifier for determining the WAN address; each of the one or more sensing devices comprises at least one sensor for sensing an event and a communications system for communicating a wireless signal for at least one of the one or more other devices of the plurality of devices at the site to perform a wakeup response comprising exiting from a low power mode, wherein each device of the one or more other devices is configured to exit from the low power mode responsive to receiving at least part of a wireless signal for the device to perform the wakeup response from a device of said sensing devices; one or more or each of the one or more sensing devices are configured to, before communicating the wireless signal for the one or more other devices of the plurality of devices at the site, transmit an event notification to the remote computing system responsive to the sensing of the event, the event notification being transmitted with one or both of: a WAN address for reaching the remote computing system or an identifier for looking up the WAN address; and the remote computing system is configured to, responsive to receiving the event notification from the one or more or each sensing device, determine at least one action parameter, the at least one action parameter comprising at least one or each of: an instruction to wake at least one of the one or more other devices; an indication of which at least one of the one or more other devices is to perform an action; and/or an indication of the action at least one of the one or more other devices is to perform; the remote computing system being further configured to communicate the at least one action parameter to at least one of the plurality of sensing devices from which the event notification was received. one or more sensing devices; and one or more other devices for performing an action commanded by the remote computing system; wherein each of the plurality of devices is configured to periodically send a proof-of-alive signal to the remote computing system on a wide area network, WAN, the proof of alive signal comprising a WAN address of the remote computing system and/or an identifier for determining the WAN address; each of the one or more sensing devices comprises at least one sensor for sensing an event and a communications system for communicating a wireless signal for at least one of the one or more other devices of the plurality of devices at the site to perform a wakeup response comprising exiting from a low power mode, wherein each device of the one or more other devices is configured to exit from the low power mode responsive to receiving at least part of a wireless signal for the device to perform the wakeup response from a device of said sensing devices; one or more or each of the one or more sensing devices are configured to, before communicating the wireless signal for the one or more other devices of the plurality of devices at the site, transmit an event notification to the remote computing system responsive to the sensing of the event, the event notification being transmitted with one or both of: a WAN address for reaching the remote computing system or an identifier for looking up the WAN address; and the remote computing system is configured to, responsive to receiving the event notification from the one or more or each sensing device, determine at least one action parameter, the at least one action parameter comprising at least one or each of: an instruction to wake at least one of the one or more other devices; an indication of which at least one of the one or more other devices is to perform an action; and/or an indication of the action at least one of the one or more other devices is to perform; the remote computing system being further configured to communicate the at least one action parameter to at least one of the plurality of sensing devices from which the event notification was received.