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On SMS Received

This block is triggered when an SMS message is received. Use it to handle text message commands and notifications from mobile phones.

On SMS Received Block

Overview​

The On SMS Received block detects incoming SMS messages on cellular-enabled devices, allowing remote control and monitoring via text messaging.

Configuration​

  • Filter: Optional phone number or keyword filter
  • Output: Variables to store message details (sender, content, timestamp)

Message Information​

Access SMS message details:

  • Sender: Phone number of sender
  • Content: Message text
  • Timestamp: When message was received
  • Encoding: Text encoding (GSM-7, UCS-2)

Use Cases​

Common SMS reception scenarios:

  • Remote device control commands
  • Emergency shutdown triggers
  • Configuration updates
  • Status query requests
  • Alert acknowledgments
  • Two-factor authentication
  • Backup communication channel

Message Filtering​

Filter incoming messages:

By Phone Number​

Only process messages from authorized numbers

By Keyword​

Trigger on specific command words

By Pattern​

Match message format or structure

Use Comparison blocks to implement filtering.

Command Processing​

Parse SMS commands:

SMS: "STATUS"
Response: Send device status

SMS: "REBOOT"
Action: Restart device

SMS: "SET TEMP 22"
Action: Update temperature setpoint

Security​

Secure SMS handling:

  • Whitelist: Only accept from known numbers
  • Keywords: Require secret keywords
  • Confirmation: Send acknowledgment SMS
  • Logging: Log all received commands

Never trust SMS content without validation.

Response​

Respond to SMS with SMS Send:

  • Acknowledge command received
  • Return status information
  • Report action results
  • Send error messages

Message Parsing​

Parse SMS message content:

  • Split into words/tokens
  • Extract command and parameters
  • Validate format
  • Handle malformed messages

Character Encoding​

Handle SMS encoding:

GSM-7​

  • Standard 7-bit encoding
  • 160 characters per message
  • Basic Latin characters

UCS-2​

  • Unicode encoding
  • 70 characters per message
  • All languages supported

Multi-Part Messages​

Handle long messages:

  • Messages > 160 chars split into parts
  • Automatic reassembly
  • May arrive out of order
  • Consider character limits

Costs​

Consider SMS costs:

  • Charges per message sent/received
  • Roaming charges
  • Data plan vs. SMS plan
  • Monitor usage

Network Requirements​

SMS requires:

  • Active cellular connection
  • SIM card with SMS service
  • Network coverage
  • Active cellular account

Integration with Features​

SMS integrates with:

Example Flows​

Status Query​

1. SMS "STATUS" received
2. Read sensor values
3. Format status message
4. Send SMS response

Remote Control​

1. SMS "TURN ON PUMP" received
2. Validate sender number
3. Set pump variable to ON
4. Send confirmation SMS

Alert Acknowledgment​

1. Device sends alert SMS
2. Operator replies "ACK"
3. On SMS Received triggers
4. Clear alarm state
5. Log acknowledgment

Error Handling​

Handle SMS errors:

  • Invalid sender: Ignore or log
  • Malformed message: Send error response
  • Unknown command: Reply with help text
  • Action failed: Send failure notification

Performance​

SMS considerations:

  • Messages may be delayed
  • Not real-time communication
  • Consider latency in design
  • Use for non-critical commands

Alternative Communications​

SMS complements:

  • MQTT: Primary cloud communication
  • HTTP: API endpoints
  • LUIS: Mobile app interface

Use SMS as backup when data connection unavailable.

Regulatory Compliance​

Consider regulations:

  • Opt-in requirements
  • Message content restrictions
  • Spam prevention
  • Privacy laws

Troubleshooting​

Common SMS reception issues:

  • Messages not received: Check cellular signal and SIM
  • Garbled messages: Check encoding support
  • Delayed messages: Normal for SMS, check network
  • Missing parts: Multi-part message issues

See Also​