Understanding ALTA Sensor Data Logging

Monnit’s ALTA Sensors offer data logging capabilities to ensure that data is saved in the event of power loss and radio communication loss. Current versions of both ALTA Sensors and ALTA Gateways offer this feature. This article will provide details on the functionality of our sensor data logging. It is also important to understand Link Mode when considering sensor data logging.

General Sensor Message Logging Behavior

Readings taken on sensor Heartbeat Intervals are logged in the sensor’s memory when the sensor is connected to the gateway, reporting data, and then loses radio communication with the gateway. 

Once the sensor reconnects, it reports current readings, then starts uploading logged readings in a manner that efficiently manages gateway bandwidth.

The number of subsequent communications depends on how long the sensor has been not communicating with the gateway, how frequent the sensor’s Heartbeat is, and how many logged data messages need to be uploaded.

Sensor Data Logging

Current ALTA Sensors log up to 2,000 to 4,000 messages. Suppose a sensor loses radio communication with the gateway (whether the sensor is moved out of range, the gateway is powered off, or other scenarios). In that case, it will log readings at its Heartbeat Interval (firmware version 14.x.x.x or later). 

The logged readings will be delivered to the gateway when the sensor reconnects to it. Uploading the data for many logged data messages can take a significant amount of time, possibly hours.

Things to consider regarding logged sensor messages:

  • The sensor must have connected to the gateway and reported data to start logging readings upon signal loss.
  • Sensors with firmware 14.x.x.x and later will retain their logged messages even on power loss.
  • Sensors with firmware 14.x.x.x and later do not offer a manner to clear logged messages, including power cycle.
  • Sensors with firmware before 14.x.x.x will log 512 messages maximum.
  • Once the sensor reaches the maximum logged messages, the sensor will halt logging, and no additional readings will be logged. In this case, there may be a gap when logged messages upload to the gateway.
  • When the sensor’s connection to the gateway is restored, the sensor will relink and upload the logged messages.

Uploading logged messages

Once the sensor relinks to the gateway and sends a current reading, it will upload the backlogged data in batches. The devices will manage the gateway’s bandwidth efficiently. 

As a result, you will likely see the gateway more active than usual, and transmissions contain more data than expected. Reviewing the sensor history will likely see backlogged data begin to show under the sensor history as it is uploaded.

Because of the higher than normal transmission activity, sensor configurations and other activities that require gateway bandwidth may be affected during logged message uploads from extended periods for multiple sensors.

It is common to have sensors that do not accept configurations during logged data uploads from any sensors on the network, especially with firmware 14.x.x.x and earlier.

Factors Affecting Sensor Data Logging

The following factors can affect sensor data logging, and you should consider them if you find your sensors did not report logged messages.

  • Sensor firmware version
  • Gateway firmware version
  • Environmental factors
  • Network configurations and linking with unexpected gateways

How this affects Rules/Alerts

An important consideration is that when sensors upload logged readings, they will trigger Rules even if the triggering reading was logged from a previous day. For example, a sensor was powered on and reporting to a gateway, but it was moved out of range of the gateway for a few days. When the sensor came back within range of the gateway, it would upload all of those logged messages. 

If the sensor reported a reading that met a rule's triggering threshold, that Rule would be triggered by the logged reading, and any associated notifications would be sent to configured recipients even though that triggering reading was recorded in the past.


Sensor data logging can be a powerful tool to ensure your data is reliable. If you have additional questions, feel free to reach out to support@monnit.com.

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