Fundamentals BroadNet answer

What is a flash SMS?

Last reviewed July 22, 20261 min readReviewed by BroadNet engineering

Quick answer

A flash SMS (class 0 message) is a text that appears immediately on the recipient's screen without being saved to the inbox by default, so it demands instant attention and disappears unless the user chooses to keep it. It is used for urgent, ephemeral alerts — critical security warnings, emergency notifications, or attention-grabbing prompts — where an ordinary inbox message might be missed or where you do not want the content stored.

Plain-language definitionVendor-neutralReviewed July 22, 2026

The long answer

Everything worth knowing, nothing that isn't.

§01

How it differs from normal SMS

A standard SMS lands in the inbox and stays there; a flash SMS (message class 0) pops up on the display immediately and is not stored unless saved. Both use the same network, just a different message-class flag. See /answers/what-is-a2p-sms.

§02

When to use it

Reach for flash SMS for genuinely urgent, time-critical, or sensitive alerts where immediacy matters and persistence is undesirable — emergency notices, fraud warnings, or one-off prompts. Overuse annoys recipients, so keep it rare.

§03

Support and limitations

Handset and network support for class 0 messages varies, so behaviour is not perfectly uniform across devices, and flash SMS is not a fit for anything the user may need to re-read later. Test on your target devices before relying on it.

§04

Alternatives

For urgent-but-persistent messages, a normal high-priority SMS on a direct route is usually the right choice; for rich urgent alerts on supported devices, consider RCS. See /answers/sms-for-payment-alerts and /answers/rcs-for-business.

BNWritten by the BroadNet engineering team·Operating carrier-grade messaging since 2003, headquartered in Dubai·Editorial standards

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