How to Send Modbus Alarms via SMS with an IoT Edge Gateway

In the Industrial Internet of Things (IIoT), data is the foundation of modern operations. We rely on a constant stream of information to monitor equipment health, ensure safety, and maintain efficiency. While cloud platforms and IP-based networks are powerful, their reliability is often at the mercy of a stable internet connection. For a remote pumping station, a cellular "dead zone," or a factory with network congestion, a lost internet connection can mean a missed critical alert, leading to costly downtime or even safety hazards.

This is where a proven, universal technology comes back into focus: SMS. By leveraging the core cellular control channel, SMS provides a highly resilient communication path that often remains active even when IP data services fail. The solution is not to abandon modern cloud platforms, but to augment them with a robust fallback. This guide will show you exactly how to build a system that sends Modbus alarms via SMS using an intelligent industrial IoT edge gateway, ensuring your most critical alerts are always delivered.

To achieve this level of reliability, you need a device on-site that can act intelligently. An industrial IoT edge gateway like the  Robustel EG5120  is purpose-built for this role. It acts as a powerful SMS Gateway for IoT , capable of:

• Directly communicating with industrial equipment via protocols like Modbus.
• Executing local logic to determine when an alarm condition is met.
• Sending alerts over multiple channels, including SMS and IP networks.

This local intelligence is the key to creating a truly resilient system that doesn't solely depend on an end-to-end internet connection.

The facility deployed a Robustel EG5120 , transforming it into a smart SMS Gateway .

1. The EG5120 was connected directly to a liquid level sensor in the tank using its RS485 interface to read data via Modbus RTU .
2. Using its built-in applications, the EG5120 was configured to monitor the water level locally (an edge computing task).
3. When the water level dropped below a critical threshold, the EG5120 instantly sent a customized SMS alert (e.g., "WARNING: Water Tank Level Low - 15%") to the maintenance team's mobile phones.
4. Simultaneously, the gateway could be configured to trigger a local digital output (DO) to activate a warning light.

This solution ensured that critical alerts were always delivered, regardless of internet status, a perfect demonstration of a Modbus alarm via SMS system.

This channel is for data logging, historical analysis, and dashboarding. At the same moment it sends the SMS, the EG5120 can publish a structured MQTT message with rich contextual data to a cloud platform like AWS IoT Core or the Microsoft Azure IoT Hub. This message could look like:

JSON

{ "timestamp": "2025-06-11T10:30:01Z", "device_id": "PUMP_A_EG5120", "alarm_type": "MODBUS_REGISTER_HIGH", "register": "40001", "value": "1", "message": "Pump A has failed" } 

This dual-channel capability provides the best of both worlds: the unmatched reliability of SMS for critical alerts and the rich data context of MQTT for advanced analytics .

This section guides you through the step-by-step process on your Robustel EG5120 .

(Note: This section's structure is preserved for easy screenshot insertion.)

Access the EG5120 WEB interface and navigate to System -> APP Center . Load the Modbus Master.rpk APP and install it.

After the reboot, the Modbus Master APP will be visible on the WEBUI under Services -> Modbus Master .

Set serial parameters according to the sensor serial specification.

Set the sensor's Modbus register address, function code, data type accordingly, and data calculation if needed.

Submit parameters, save and apply. The EG5120 communicates with sensors via Modbus, and their readings are displayed on the status page.

Navigate to the SMS Alarm settings. Here, you can define the alarm trigger conditions (e.g., equal, unequal, less than, greater than the setpoint) and set a Hysteresis value if needed to prevent rapid toggling. You can also specify the phone numbers that will receive the SMS alerts.

More than 30 phone numbers can be configured to receive the alarm, and the alarm content itself is fully customizable, allowing you to include specific sensor readings or contextual information.

While this guide focuses on a Modbus alarm via SMS , the capabilities of the EG5120 as an SMS Gateway extend to many other applications:

• Remote Device Control: Send an SMS command (e.g., REBOOT_SYSTEM) to remotely restart the gateway or trigger a connected device via its digital output.
• System Status "Heartbeats": Configure the gateway to send a daily or weekly "I'm alive" SMS to a central number, providing confidence that remote, unmonitored sites are still operational.
• Security Breach Alerts: Use a digital input connected to a door sensor. If a cabinet is opened unexpectedly, the gateway can instantly send an SMS alert for a potential security breach.
• Network Failover Notification: Configure the gateway to send an SMS alert when it switches from its primary Ethernet connection to its 4G cellular backup, notifying IT staff of a primary network failure.

While cloud platforms are central to modern IoT, relying on them alone for critical alerts is a risky strategy. By leveraging the universal reliability of text messaging, an SMS Gateway for IoT provides an essential layer of resilience. The Robustel EG5120 demonstrates how a modern industrial edge gateway can masterfully integrate both old and new technologies—combining direct Modbus communication with reliable SMS alerting and powerful MQTT data integration. For any organization deploying mission-critical systems, implementing a solution for sending Modbus alarms via SMS is not a step backward; it's a smart step forward into building truly robust and reliable operations.