Lowest cost SMS for ESP32

[rcbuck]

I have an ESP32 project that I may want to send 1 or 2 text messages per day to my phone. The ESP32 monitors a process and returns data to a small LCD screen.

If the process has a problem I want to send an alert to my Android phone. Does anyone know of a low cost (no monthly fee, no SIM card) SMS provider that charges a fee on a per message basis? The application may go several days without sending a message. The message would only be sent to my personal phone.

Or would AWS be the best way to handle this? The application does have access to my WiFi network, which means it can access any online service.

[Peabody]

I recently finished an Arduino project that used an ESP8266.  It is a daily check-in device for seniors who live alone.  If the senior doesn't check in to the device (push a button) by the set time, the device triggers a push notification to the cell phone of a relative.   The Pushover service is used for this (pushover.net).  This is transmitted over Wifi, so no cellular data service is needed.  The cost is a one-time lifetime fee of $4.99 for each device which is to receive the notifications.

Since you have Wifi, I would strongly suggest you take a look at Pushover.  It seems to be perfect for what you have in mind, and the cost, which is all upfront, is minimal.

The code for the ESP32 should be very similar to my ESP8266 code.  I also used the WiFi Manager library to obtain WiFi credentials and Pushover keys, but you could just hard code them.  Here's the project:

https://github.com/gbhug5a/Daily_Check-In_Device

[rcbuck]

Peabody, thanks for the tip and link. I will check it out. It sounds like it may be what I am looking for.

[Doctorandus_P]

SMS without SIM card? My first guess would be that a pre-paid SIM card  is probably the most attractive, but I'm living on the other side of this world.

Maybe LoRa / LoRaWAN can be interesting.
https://en.wikipedia.org/wiki/LoRa

[Peabody]

I should have said that Pushover gives you a 30-day free trial (no credit card), so you have plenty of time to see if it works.  One more point.  Somewhere in the ESP32 library is a function called setInsecure().  You'll have to use an encrypted HTTPS connection to the Pushover server, but setInsecure() lets you do that without checking the server's certificate.  And that in turn means you don't have to check certificates or fingerprints as they change from time to time.  There's a push to give certificates shorter and shorter lives.  That's going to become a problem for embedded stuff if you have to check the certificate.  But for sites like this, you really don't need to do that.

[rcbuck]

Peabody, I installed Pushover on my desktop and on my Android phone. It is working fine and will do what I need it to do. The onetime $5 charge can't be beat.

I created a Bash script on my Linux server to send messages to the Android. It works exactly as intended.

I also found that I can send an email to the pushover email address and that also works properly. That is probably how I will implement it on my ESP32 as I already have email working on the device.

Thanks for the suggestion.

[Peabody]

Glad you got it working.  I think you will find it to be very reliable.

[negativ3]

Push Notifications via ntfy.sh.

Install the free ntfy app on your phone and create a unique topic (e.g., myesp32alerts).
On the ESP32, use HTTP POST to send messages to https://ntfy.sh/yourtopic.
The message appears as a native push notification on your phone.

Pros: Very easy, no account needed for basic use, works cross-platform.
Limits: Free tier has ~250 messages/day.

Good for sensor alerts, door open, temperature warnings, etc.