TAP — Telocator Alphanumeric Protocol — is the industry-standard protocol for sending short text messages from remote equipment to a messaging provider over a phone-line modem. Born in the paging era, it found a second life in the UK alarm industry: intruder panels, fire systems and industrial monitoring kit use it to tell an engineer "something's wrong" by SMS.
Sources: Telocator Alphanumeric Protocol (Wikipedia); DIDcomms OpenTAP documentation.
Why TAP refuses to die
Because of what it doesn't need: the internet. A TAP transmission is a plain modem call. No router, no static IP, no firewall config, no app credentials. For security-critical signalling, a protocol that works on a copper pair has been the dependable default for decades — cheap panel modems still speak it, and engineers know it.
How a TAP-to-SMS gateway works
- The alarm panel's modem dials the gateway's access number over the phone network.
- The gateway answers the call and speaks TAP with the panel: handshake, message blocks, checksums.
- The gateway decodes the message and delivers it as an SMS to the engineer's mobile, with logging.
Instead of each mobile network running its own TAP gateway with its own access number (the old paging-era arrangement), a modern gateway like DIDcomms' OpenTAP gives you one access number that reaches any UK network.
The settings that decide whether it works
TAP uses 7E1 serial framing — the single most common reason a TAP connection "connects but never delivers":
| Setting | Required value |
|---|---|
| Baud rate | 1200 |
| Data bits | 7 |
| Parity | Even |
| Stop bits | 1 |
Many modems ship as 8N1 (8 data bits, no parity, 1 stop). If your panel is set to 8N1 the call will appear to connect but messages will never decode correctly — check the panel's paging/TAP serial settings against the table above.
The 2027 problem — and the fix
TAP rides on dial-up, and dial-up rides on the PSTN, which closes on 31 January 2027 (see our PSTN switch-off guide). Alarm signalling is one of the switch-off's most-affected services, so every TAP deployment needs a plan:
- Keep the panel, change the transport: put the panel's connection on an IP path. OpenTAP supports TAP over TCP/IP — the panel (or a small adapter) sends its TAP session over the internet instead of a modem call.
- Budget for it honestly: OpenTAP's TCP/IP option is pay-as-you-go at 5p per message inc VAT with no subscription — and the dial-up access numbers carry no monthly fee either.
- Test before the copper goes: re-programme one site, confirm delivery logs, then roll out. OpenTAP's published access numbers are 09018 600011, 09117 329997 and 07640 177177.
Choosing a TAP gateway
- Coverage: delivers to all UK mobile networks from one access number
- Logging: timestamp and delivery-status records you can show an insurer
- Pricing model: per-message PAYG beats subscriptions for low-volume alarm traffic
- IP route: TCP/IP support is your switch-off insurance
- Support: someone who knows 7E1 from 8N1 when you're on a ladder at 4pm on a Friday
DIDcomms' OpenTAP ticks all five and is used by thousands of UK installations — see OpenTAP on didcomms.co.uk.
FAQs
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