Charities warn domestic abuse victims could be put at risk by the upcoming national emergency alert drill, as its sound may reveal hidden phones.
On Sunday, 7 September at around 3pm, 4G and 5G mobile phones will vibrate, emit a siren for up to 10 seconds, and display a message confirming the drill.
The audible alert raises concerns that it could inadvertently expose hidden devices, prompting groups to issue opt-out guidance.
To opt out, iPhone users should go to settings, search for “Emergency Alerts”, and turn off “Severe & Emergency Alerts”.
Android users can do the same by searching “Emergency Alerts” in settings and switching off “Severe & Emergency Alerts”.
Meanwhile, theatre-goers are advised to turn off their phones, and drivers are urged not to be distracted if behind the wheel when the alert takes place.

Emma Pickering, of charity Refuge, said: “During the initial roll-out of the Government’s emergency alert system, Refuge expressed concerns about how the alerts could indirectly impact survivors who have hidden devices by making their abuser aware of the device.
“We must be clear – abuse is always a choice a perpetrator makes, and technology itself is not responsible.
“When used correctly and as intended, technology can make vast improvements to our lives, and we know that having a hidden device that can be used to access support without fear of being tracked can offer a lifeline for many survivors.
“However, in the hands of a perpetrator of abuse, technology becomes another tool to misuse and weaponise, often with devastating effects.”
A spokesperson for women’s aid charity Solace said: “These alerts may put domestic abuse survivors at risk, if they are concealing devices from perpetrators.
“Survivors may hide devices because they use them to seek and receive support, or to seek employment to increase their financial independence.”
Society of London Theatre (SOLT) and UK Theatre said its members have been advised about the alert.
A spokesperson said: “Theatres are updating their pre-show announcements to remind audiences to turn phones off completely, helping to minimise disruption.
“Theatre is a uniquely live experience where the unexpected can happen – but it’s always best when the surprises come from the stage.”
The AA recommended that drivers familiarise themselves with the alert sound and vibration and do not interact with the message until stopped in a safe place with the engine switched off.

Edmund King, AA president, said: “We support the testing of the emergency alerts system, which is an important tool the Government uses to keep people safe in a crisis.
“On the day, drivers should simply stay calm and focus on the road. As always, only check your phone when you’re parked safely with the engine turned off.”
RAC road safety spokesperson Rod Dennis said: “Anyone driving on Sunday afternoon needs to be ready for the 3pm emergency alert test, so we’d encourage people to share the message far and wide with anyone they know.
“The loud siren-like sound that will be emitted by millions of phones is, of course, designed to get everyone’s attention but it’s important drivers stay focused while it’s going off for 10 seconds or so.”
A National Highways spokesperson said: “We are displaying messages on some of our motorway signs to tell motorists about the national emergency alert test on Sunday September 7.
“We are also displaying other safety messages, as well as incident updates as usual.”
The system is designed for use during the most likely emergencies to affect the UK and warnings would also be transmitted on television, radio and locally by knocking on doors.
Pat McFadden, Chancellor of the Duchy of Lancaster, said: “On Sunday September 7 we will hold a UK-wide test of the emergency alerts system to ensure it works when we need it most.
“It is a vital tool for keeping the nation safe when lives are on the line – and every minute matters.
“During Storm Darragh and Storm Eowyn, as millions faced dangerous extreme weather, I saw first-hand how effective it was at getting life-saving advice to at-risk communities in an instant.
“We do not use the system often, but like the fire alarm in your home, it is always on standby should we need to act.”