Will my phone work in a power cut?
In brief
- Digital landlines do not work in a power cut unless your router has battery backup.
- The old analogue system powered the phone line itself. The new system does not.
- A mini UPS (from around £25) can keep your router running for several hours.
- Keep a charged mobile phone as a backup. Join the Priority Services Register if you are vulnerable.
The short answer
If your landline goes through your broadband router (or a fibre box), it will not work in a power cut unless that equipment has battery backup. This is a change from the old analogue system, where a basic corded phone could draw power from the phone line itself.
Why the old system worked differently
The traditional analogue phone line (PSTN) carried its own small electrical current. A simple corded phone, with no mains plug, could work even when the power was off. That is how many people kept a phone line during power cuts for decades.
Cordless phones (with a base station that plugs into the mains) have never worked in a power cut, even on the old system. Only a basic corded phone plugged directly into the wall socket would work.
What needs power on a digital landline
On a digital voice service (also called VoIP, or an IP-based landline), your voice is carried over the broadband connection. That means the following equipment must all have power for a call to work:
- Your broadband router or hub: this is the main box your phone connects to
- A fibre box (ONT): if you have a full-fibre (FTTP) connection, there is usually a separate small box where the fibre enters your home. It also needs power.
- A phone adaptor: some providers use a small adaptor between the router and the phone. This needs power too.
- The phone itself: if you use a cordless phone, the base station needs power. A corded phone plugged into the router's phone port does not need its own mains supply, but the router still does.
If any one of these loses power, the landline stops working.
What about mobile phones?
A mobile phone works independently of your home power supply, as long as it has battery charge and there is a mobile signal. In most power cuts, the mobile network continues to work because the masts have their own backup power (typically lasting several hours).
However:
- In a widespread or prolonged power cut, mobile masts can also lose power.
- Mobile signal may be weak or absent in some areas, particularly rural locations.
- If your mobile battery is flat, it will not help.
Keep your mobile phone charged. A power bank is a simple and inexpensive backup.
What providers must do
Under Ofcom's rules, phone providers must make sure customers can contact the emergency services during a power cut. Providers must offer at least one solution, which could include:
- A battery backup unit that powers your router for a limited time (typically one hour)
- A mobile handset with enough charge and credit to make an emergency call
- Call diversion to a mobile number
These solutions vary between providers. Some offer them free of charge to all customers; others provide them only to customers on the Priority Services Register or those who specifically request one.
What you should do
- Check your setup. Follow the phone cable. If it goes into the broadband router (not a wall socket), your landline depends on mains power.
- Ask your provider what happens in a power cut. Call them and ask: "What solution do you offer for making emergency calls during a power cut?" Write down the answer.
- Keep a charged mobile phone. This is the simplest backup for most people.
- Consider a battery backup if you depend on the landline, for example if mobile signal is poor, or if you use telecare or a personal alarm that goes through the router. See router power backup setup for a step-by-step guide.
- Join the Priority Services Register if you are elderly, disabled, chronically ill, or in another vulnerable situation. Your energy supplier and phone provider both have registers. Being on the register means you should get extra help during outages.
If you rely on a personal alarm or telecare
Telecare devices (pendant alarms, fall detectors, epilepsy monitors) that connect via the phone line are particularly affected. If the router loses power, the alarm cannot reach the monitoring centre. This is a safety risk, not just an inconvenience.
Read our dedicated guide: Telecare and personal alarms. You can also use the device risk checker to see which of your devices are affected.
If you are helping a relative or neighbour prepare, see for carers and families.