Thursday, June 13, 2024

GSM-based SOS Alert Device

ashwiniThe safety of children, elderly people, medical patients and women is a prime concern, whenever they are outside or at home alone. Nobody wants anything unfortunate to happen. The good thing is that communication networks have improved, leading to an increased usage of phones and the internet. But what if these people wish to quickly or discreetly inform about their whereabouts for help. A smartphone is not preferable in such a situation as one has to dial a long sequence of digits. 

So, in this project, you will learn to design a small device like a wristwatch or any other small switch that can immediately send an SOS alert when in need of urgent assistance. The device will be equipped with a GSM module such as SIM800L or any other microcontroller-based GSM module. At the press of a button, the person will be able to send a notification seeking help.

Bill Of Materials 

Let’s start designing our device with the shopping of the following components:


For programming the RP2040 board, open the Board Manager in Arduino IDE and install the MBED OS-based dev board.

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Because you will be also using the GSM SIM800L module, install the FONA library from the Library Manager in Arduino IDE.


After installing the FONA library, set the hardware serial number for using the SIM800L module. Use serial 1 of RP2040.

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Then create a setup function for initialising the serial 1 communication with a baud rate = 4800 (default baud rate of SIM 800L).

Next, create a loop function for checking whether the notification switch/button is ON or OFF. When ON, a help message is sent to the desired phone number.


Connect the modules as shown in the connection diagram. Assemble everything in an enclosure.


Finally, insert a 2G-enabled SIM in the SIM800L module. Power the device and wait a few seconds for it to get connected to the network. Whenever you press the ON button, the device will send an SMS alert to the set phone number.

Congrats!! You have successfully built the GSM-based SOS alert device. It can now be used for alerting your parents, friends or loved ones when you are in danger.

Download Source Code

Ashwini Sinha
Ashwini Sinha
A tech journalist at EFY, with hands-on expertise in electronics DIY. He has an extraordinary passion for AI, IoT, and electronics. Holder of two design records and two times winner of US-China Makers Award.


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