Documentation  〉SMS alerts

SMS alerts are complicated, due to wide variety of operators worldwide and the unstability of routes. So we of course can't guarantee deliverability but will try our best. We're using various providers and method of sending in order to optimise deliverability. For example if one country is not reachable any more through one provider, sometimes another provider has a better route and can still deliver.

What number will the SMS come from?

Initially we were sending most of our SMS alerts with the sender ID, this usually looks nice (unless your carrier doesn't support it and replace with another number) but it unfortunately doesn't play well with "Do not disturb" mode as you can't exclude from it (it needs to be a real number). So we've changed this to long numbers so you can add it to your contacts if you want to give it a name and you can also exclude it from "Do not disturb". Also we added a prefix to all SMS messages: [updown alert], so there will be no confusion as to who sent this now that the sender ID can be a number.

The sender ID may change depending on your country due to local operator constraints:

Country code Sender ID
CA, IL, PR, US +18445900909
GB +447480635284
FR¹, NZ, SA +33745102477
All other countries +33644633396

¹only some numbers, the rest will see +33644633396.

Note that some operators in some countries will require to change the Sender ID to ensure delivery so you may receive SMS from another sender. Also we may change provider or senderID to improve deliverability at some point, we'll try to keep this list up-to-date when this occurs.

Why do alert SMS fails but the test SMS works?

When this occurs, most of the time the network operator rejecting the SMS won't tell us why, but usually this is caused by their "anti-spam" protection rejecting the SMS simply because it contain a URL. So in this situation we recommend setting an Alias on your check that would be used instead of the URL in alert messages.

For example instead of you could set the Alias mail example, mail server or whatever sounds unique enough for you to distinguish between your checks. Sometimes just using the hostname as an Alias works, but that would depend on the operator "anti-spam" implementation of course.

To test this new configuration, you can either:

  1. Set the Contains attribute temporarily to something random (ex. 192837) to trigger an alert (as string will not be found on the page) and then change it back. You can also reduce the check frequency temporarily to perform this test quicker.
  2. If you don't want to generate a fake downtime on your existing check, you can create another one with a similar URL and Alias (just change one or two chars to make it unique and invalid), wait for the alert and then delete it. (example:

Adrien Rey-Jarthon
Created on November 05, 2023 · Last update on January 04, 2024 · Suggest changes to this page