Sensor with an alarm, not updated recently must trigger kadonnut alarm

If a sensor is configured to alarm on a limit and it hasn’t been heard from in 3 times normal interval (+/-?) a “missing sensor” alarm must be displayed by station and an email sent.
For example a sensor configured with temperature low limit at 0C and no station or gateway has received a packet from it in 1 minute(+/-?) its battery may have been exhausted, it may have gotten wet or ben damaged or maybe something is blocking the radio.