Can I enable a sensor to receive downlinks at any time?
A downlink message is one that is sent to the sensor from the cloud and is used to configure the sensor itself.
For Class A devices, messages cannot be initiated from the cloud since the sensor is typically sleeping and the radio is turned off, so the sensor itself must initiate a downlink message. The Supervisory Message Event, Device Reset, and Tamper-Open (not Tamper Close) messages all request a downlink message as a response, and the response must be received within 30 seconds of the request.
A Class C device could be configured to always be in receive mode and would therefore be able to receive a Downlink Configuration message at any time. Such a device would need to be externally powered due to the increased power requirements and battery operation would be generally infeasible.
A possible workaround for a Class A Sensor which would enable it to receive downlinks more frequently and independently would be to increase the frequency of the Supervisory Message. For example, a Supervisory Period of 15 minutes would allow the sensor to enter receive four times an hour in order to check for and receive new downlinks at the expense of overall battery life.
As of Firmware Version 1.3 the Supervisory Period can be set anywhere between 1 minute and 127 hours.