When most businesses hear about the PSTN switch‑off, they assume it’s just about replacing phone handsets but that’s only part of the story.
Across the UK, thousands of organisations are discovering that critical systems they rely on every day still use traditional phone lines in the background.
When those lines are switched off, these services can stop working – often without warning.
This article explores the lesser‑known systems affected by the PSTN switch‑off, and where unexpected disruption could occur if they’re not identified early.
A quick reminder: what is the PSTN switch off?
The PSTN (Public Switched Telephone Network) is the UK’s old copper phone network. It’s the system that has powered landlines for decades, but it’s now being permanently retired.
The final switch‑off date is 31 January 2027. After this date, PSTN and ISDN services will no longer work. This is a nationwide change led by Openreach, not individual telecoms providers.
Crucially, PSTN isn’t just used for phone calls. Over the years, it became the default connection for many business‑critical systems – often installed and then forgotten about.
You can learn more about the PSTN switch off here.
Alarm and security systems
One of the most common and serious oversights is alarm systems.
Many intruder alarms, fire panels and monitoring systems still use PSTN lines to “dial out” to monitoring centres. When PSTN is switched off, these systems may no longer be able to send alerts, even though the alarm itself still appears to work.
This can create:
- Security blind spots
- Insurance and compliance risks
- A false sense of safety
Alarm providers and industry bodies have repeatedly warned that PSTN‑based signalling must be replaced with IP or mobile‑based alternatives well before 2027.
Card payment machines (EPOS)
Some card payment terminals still rely on phone lines, particularly in:
- Small retail businesses
- Hospitality venues
- Backup or failover setups
If a PSTN‑connected EPOS terminal loses its connection, payments can fail entirely. For customer‑facing businesses, that can mean lost revenue and frustrated customers at the till.
Even where broadband‑connected terminals are in use, it’s important to check whether any fallback line still relies on PSTN. BT has compiled a list impacted services here.
Lifts and emergency phones
Lift emergency phones are a safety‑critical example of hidden PSTN usage.
Many lift auto diallers rely on traditional phone lines because they historically drew power directly from the copper network. Digital phone services work differently and don’t provide the same power or signalling characteristics.
If these systems aren’t upgraded correctly, there’s a risk that emergency calls won’t connect in the event of a fault or power cut.
Industry guidance is clear that lift lines must be assessed separately and migrated to appropriate alternatives, such as mobile‑based solutions, ahead of the switch off.
CCTV and monitored systems
Some CCTV and monitoring systems use PSTN lines to:
- Send alerts to monitoring centres
- Provide out‑of‑hours connectivity
- Act as a backup communication path
Once PSTN is switched off, these systems may lose their ability to communicate externally, even though cameras continue recording locally.
This can leave businesses assuming they’re protected when alerts are no longer being transmitted.
Door entry and access control
Door entry systems and intercoms are another commonly overlooked area.
In many buildings, especially older offices and multi‑occupancy sites, these systems rely on analogue phone lines to connect visitors to reception desks or mobile phones.
When PSTN goes away, calls may fail or not connect at all. This can affect both security and day‑to‑day operations.
Broadband services tied to phone lines
Finally, it’s important to consider broadband.
Older broadband technologies such as ADSL – and some FTTC services – rely on PSTN lines. When those lines are withdrawn, broadband may also need to be upgraded or re‑provisioned.
This is often discovered late, when a phone line is removed and broadband unexpectedly stops working as well.
How businesses can reduce the risk of the PSTN switch off
The biggest risk with the PSTN switch‑off isn’t the technology – it’s not knowing what’s affected.
Businesses that reduce disruption tend to follow the same approach:
- Audit every phone line and connected service
- Identify which systems rely on PSTN, even indirectly
- Plan replacements early, rather than reacting later
This is particularly important where safety, security or customer payments are involved.
In simple terms
Most people hear ‘PSTN switch off’ and think phones. But there’s a whole layer of services ticking away in the background that you’ve probably never had to think about
If even one of those services is missed, the impact can be immediate.
The good news is that with early visibility and the right planning, most businesses can transition smoothly – often improving resilience at the same time.
If you’re looking for a partner to work with you to ensure you’re ready for the PSTN switch off, why not reach out and speak with our team today?
Frequently Asked Questions: Hidden Services & the PSTN Switch Off
What kinds of “hidden services” rely on traditional phone lines?
Many businesses are surprised to learn that traditional phone lines aren’t just used for calls. They’re often used by alarm and security systems, card payment machines (EPOS), lift emergency phones, door entry systems, CCTV monitoring and even some broadband connections. These systems are often installed once and left untouched, which is why the risk can go unnoticed.
Why is this a bigger risk than just replacing phones?
Phones are obvious – if they stop working, you notice immediately. Hidden services are different. An alarm, lift phone or CCTV system may look like it’s working locally but fail to communicate externally once PSTN is switched off. That can create safety, security or compliance issues without any clear warning signs.
How do I know if my business is affected?
If your business has older alarms, card machines, lift phones, intercoms, fax lines or older broadband, there’s a good chance PSTN is involved somewhere. Phone bills that mention line rental, analogue lines, PSTN or ISDN are another strong indicator. In many cases, the only reliable way to know is to carry out a full audit of phone lines and connected systems.
What happens if one of these services isn’t upgraded in time?
If a system still relies on PSTN when the network is switched off in January 2027, it will stop working. That could mean alarms failing to alert monitoring centres, card payments being declined, lift emergency phones not connecting, or CCTV alerts not being sent. In some cases, this can also affect insurance cover or regulatory compliance.
What should businesses do now to reduce the risk?
The most important step is visibility. Businesses should identify every phone line and understand what’s connected to it – not just phones. From there, affected systems can be upgraded or replaced with digital or mobile‑based alternatives. Starting early allows changes to be planned calmly, rather than reacting when a service suddenly stops working
