ALTA Wireless Sensor and ALTA Gateway Handshake

When a Monnit ALTA Sensor first connects to an ALTA Gateway, it performs a startup test to check its hardware and initiate communication with it. An ALTA Sensor sends 10 consecutive communications 30 seconds apart when this occurs. Once this handshake completes, the sensor goes back to its configured Heartbeat. With default configurations, the default Heartbeat is 120 minutes.

Sensor Handshake
Sensor Handshake

Consideration when using the ALTA Serial MODBUS Gateway or SNMP/MODBUS TCP Interface of the ALTA Ethernet Gateway

In the iMonnit online portal, it’s easy to see the Heartbeat configuration of a sensor. The default Heartbeat of a sensor is 120 minutes, so after the sensor completes its handshake, it returns to its default 120-minute Heartbeat. Under the sensor’s Settings tab, you can see that it is generally clear that this is the case. However, when operating a sensor with an independent interface such as the ALTA Serial MODBUS Gateway or the SNMP/MODBUS TCP Interfaces of the ALTA Ethernet Gateway, the handshake and Heartbeat configuration may be confusing. A new user can be confused by the handshake with 30-second communication followed by a longer period without communication when the sensor returns to its default Heartbeat.

This is an important consideration when first connecting a sensor to a gateway with a standalone configuration. The sensor will perform the handshake (10 communications 30 seconds apart) and return to its default Heartbeat (120 minutes). You may want to enter a different sensor Heartbeat configuration, power the sensor off for 60 seconds, and power it on so the sensor retrieves the new Heartbeat. The sensor will perform its handshake and should accept its Heartbeat and start checking in with that configured interval.


When a sensor performs a handshake, the self-test bit is set to true. This means your sensor will have a distinct Aware Status when completing the handshake. This status can often indicate a specific issue during the self test. Common Aware Statuses are 1, 3, and 17.

Changes to the handshake procedure

Over the years, the handshake procedure has changed. Therefore if you have an older Generation 1 sensor, it may not perform a handshake when it communicates multiple times. Some older Gen1 and ALTA Sensors perform a handshake when they communicate four times, 30 seconds apart. Current ALTA Sensors check in 10 times.

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