PSTN Replacement Guide

PSTN Alarm Dialler Replacement Using 4G GSM Diallers

The UK PSTN network is being phased out, meaning many traditional alarm diallers, speech diallers and early 2G/3G alarm communicators will soon stop working reliably over analogue phone lines. Modern 4G and 5G IoT alarm diallers such as the CQ5 provide a future-proof replacement with secure VPN connectivity, SMS, email and remote monitoring support.

If your alarm system currently relies on:

• Public Switched Telephone Network (PSTN)
• Analogue Phone Lines
• Landline diallers
• Speech Diallers
• 2G/3G signalling
• Legacy Redcare-style systems

it will require upgrading to a modern 4G cellular alarm communicator before the switch-off deadline in January 2027.

Priory Access manufactures UK-designed 4G and 5G-IoT alarm communication systems designed for reliable remote monitoring, SMS alerts, access control and industrial telemetry.

What Is The PSTN Shutdown?

The Public Switched Telephone Network (PSTN) has been the backbone of UK analogue telephone systems for decades. In the beginning we had the 'operator' who literally switched calls between phones using a cable with plugs on it!

Obviously that was never going to be a long term solution for connecting the world. Much better was the electromechnical 'Strowger Switch'.

If you're as old as me, you'll remember those phones with rotary dials that made a clicking noise with the number of clicks corresponding to the number you dialled. All this was doing was briefly disconnecting the phone line as it clicked which would advance a rotary switch with every pulse. You would do this typically 7 times to dial a local phone number which would in turn connect your phone to the remote one.

With every home and business having a phone and sometimes a fax machine too, eventually local numbers like my own family's phone number, 051 428 9808, were facing exhaustion. So in 1995 we had phONEday - a day so exciting even the teenage me remembered it!

For my family it was easy - our 051 Liverpool number just became 0151 making the young me wonder why it was even necessary, but for people in regions such as Sheffield... Well it seems obvious now what the change was for. Their 07421xxxxx numbers became 01141xxxxx with the old numbers looking a lot like modern mobile numbers.

But don't worry in Liverpool we did suffer. One of our exciting night time venues the '051' became the butt of a tedious on-going joke for obvious reasons.

The switchover to longer phone numbers had the effect of killing off any remaining electro-mechanical exchanges as there were not enough relays for the longest numbers. By then they were almost all digital control of digitised audio.

Modern day telecoms is digital from the moment the audio hits the microphone. Speech passes through the internet just like any other data. Exchanges are software and the burdensome analogue system is used less and less and will soon be finished. Anything that relies on analogue audio signalling such as the ADE Informa Speech Dialler, Texecom CGC-0001 or SD1 speech dialler will eventually stop working on post-PSTN networks.

This affects many:

• Alarm systems
• Auto diallers
• Gate controllers
• Lift emergency phones
• Intercoms
• Remote monitoring systems
• Telemetry equipment

Older systems that depend on analogue tones or legacy line voltages will stop operating once migrated to digital voice services.

Why 4G & 5G Alarm Communicators Are Replacing PSTN

Modern cellular alarm communicators provide a direct connection via the mobile network rather than relying on landline infrastructure.

Why Many Early 4G Alarm Diallers Are Already Obsolete

Priory Access make both a standard telephone SIM dialler and an IoT Alarm dialler. What's the difference you may ask?

The IoT dialler has a multinational, multinetwork SIM card that can operate across several technologies, on multiple networks in multiple countries. In the UK for example, we have access to EE 2G, 4G, NB-IoT, and LTE-M bands - that's 4 different EE networks for 1 operator and in the UK we have access to all 4 operators. In total, in the UK, these SIM cards give access to 14 networks from 3, EE, Vodafone, and O2.

A traditional mobile phone SIM based unit has access to just 2 technologies on one network at best. But there is another more insidious problem: VoLTE and IMS SMS.

Voice over LTE (VoLTE) and the IP Multimedia Subsystem (IMS) are the protocols modern phones use to make calls and send SMS. Mobile phone technology is not as simple as it first appears. 2G, 3G, 4G and 5G are not completely separate systems but a progressive evolution of telecoms standards defined by 3GPP release numbers. Indeed there are such big steps between technologies we even have things like 2.5G, 3.5G and 4.5G/4G+.

The first '4G' release was release 8 in 2008. This version of 4G was data only with no consideration to making calls or sending SMS. This was all handled by 2G and 3G which still featured on these radios. The first VoLTE release came with release 10 and is the minimum requirement for VoLTE - 4G calling. A lot of networks require a later spec; notably Vodafone who require a 3GPP 12+ release for VoLTE. Old phones and diallers are usually not compatible with Vodafone's 4G calling system. 

On these '4G' phones SMS and calls are performed by 2G or 3G. The first major 4G modem, which is the heart of all cellular diallers and SMS senders, used a release 11 chipset made by Qualcomm. This offered 4G calling and SMS if correctly set up on simple 4G networks like those offered by 3UK and EE. The trouble is, most early '4G' diallers were not set up correctly and, even if they were, are simply not compatible with modern networks.

Many early “4G” alarm diallers still depend on legacy 2G fallback for SMS and calling. As 2G networks are eventually retired, these diallers will stop working properly despite being marketed as “4G”.

CPaaS Services

There is another way; use a communication service to send the SMS and make the calls directly from the carrier. 

Given the complexity of 4G calling and SMS, and the resource limitations of a simple modem, using a CPaaS service makes so much sense. All of the complexity is moved to powerful datacentre servers leaving the dialler as a simple data terminal. This is how our 4G/5G-IoT Alarm Diallers work. All of the telecoms happen in the cloud allowing for advanced modes and multilingual text to speech.

This is why only Priory Access IoT diallers are designed to provide the reliability modern critical alarm systems require.

Upgrade Existing Alarm Systems Without Full Replacement

In many cases, the entire alarm system does not need replacing.

A cellular communicator can often be connected to an existing alarm panel. Our 4G & 5G-IoT alarm diallers have analogue input terminals allowing them to be simply connected to the analogue bell terminal of your alarm panel - this is the terminal on your alarm that tells the bell to ring.

This allows older infrastructure to continue operating while upgrading the communication path to modern 4G or 5G connectivity.

Applications For Cellular Alarm Communicators

4G and 5G alarm diallers are increasingly used for:

UK Manufactured IoT & Alarm Systems

At Priory Access & Alarm Diallers, we develop and manufacture advanced cellular IoT and alarm communication systems in the UK.

Our systems support:

• 4G & 5G connectivity
• SMS & email alerts
• Remote access control
• Industrial telemetry
• Zigbee integration
• GPS monitoring
• Custom automation
• Cloud connectivity

We also offer flexible solutions for installers, OEM applications, industrial integration and bespoke monitoring projects.

Future-Proof Your Alarm System

As analogue phone services continue to be retired, upgrading communication systems is becoming increasingly important.

Modern 4G and 5G alarm communicators can provide:

• Improved reliability
• Remote management
• Enhanced functionality
• Future network compatibility

Whether you are replacing a simple PSTN dialler or upgrading a larger industrial monitoring system, cellular connectivity offers a modern alternative to legacy phone-line signalling.

Frequently Asked Questions

Will my existing telephone line alarm stop working after the PSTN shutdown?

Some systems may continue to operate temporarily on digital voice adapters, but many older diallers experience reliability issues or incompatibility.

Can I upgrade without replacing the whole alarm?

In many cases, yes. Existing alarm panels can often be retained while replacing only the communication method.

Do cellular alarm systems need broadband?

No. Cellular alarm communicators operate using the mobile network.

Can alarm systems still send SMS alerts?

Yes. Modern GSM/4G/5G communicators commonly support SMS, email and app notifications.

Will old “4G” alarm diallers continue working after 2G shutdown?

Not necessarily. Many early “4G” diallers still rely on 2G fallback for SMS messaging and voice calling because they do not fully support modern VoLTE and IMS standards.

Are 2G and 3G alarm systems obsolete?

In the UK 3G is already gone as is the case in many EU countries. 2G is still around but is becoming increasingly unreliable. 4G and 5G systems provide better future compatibility and much better reliability - so long as they're well designed!

Need Advice On Replacing A PSTN Alarm Dialler?

If you are upgrading an existing alarm, gate controller or telemetry system following the PSTN shutdown, we can help recommend suitable 4G or 5G alternatives.

Explore our range of cellular alarm communicators, IoT monitoring systems and remote access solutions or contact us for further advice.

https://www.alarm-diallers.com/products/4g-gsm-alarm-dialler-sms-sender-and-emailer-for-intruder-and-fire-alarm-panels