The UK's Emergency Alerts system - due to be tested on devices on Sunday - would be used for real to warn the population of an imminent danger to life.
But, for victims of domestic violence and those enduring controlling and coercive behaviour, this weekend's test could alert an offender to the very presence of a mobile phone or tablet kept hidden.
Now police and charities have issued an urgent warning to anyone in that situation ahead of the test at 3pm on Sunday.
Compatible smartphones and tablets will display the alert message on screen, make a distinctive piercing siren sound for 10 seconds and vibrate.
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The sound is designed to be attention-grabbing and will override normal volume settings. It's designed to alert a recipient even when a phone is on silent or they are in a noisy environment.
Not all devices will receive the alert. Older phones or those not connected to 4G or 5G networks may not be compatible with the system.
Detective Superintendent Jen Tattersall is Greater Manchester Police's lead for domestic abuse. She said: "There is a lot of awareness now about the alert that is going to be issued on mobile devices on September 7.
"Some people do have different devices that other people do not know about. If you are a controlling and coercive behaviour victim and you have a main device that your partner knows about, you may also have another device that maybe they don't know about which you can use to contact people that you feel are safe.
"It's just making sure that you are aware of that date and if need be, that you turn off any alerts on that device if it's going to put you in danger or put you at risk.
"We would only say to turn that alert off for that process. What we wouldn't want is somebody to be alerted to a device that a perpetrator doesn't know about.
"Some people do have a device that their partner doesn't know about. What we wouldn't want is two devices to ping in the presence of an offender."
To opt out of the test, people with iPhones can go to the settings function then search for 'emergency alerts' and turn off 'severe & emergency alerts'.
Android users should search for 'emergency alerts' in the settings profile and switch off 'severe & emergency alerts'.
The Domestic Abuse Commissioner for England & Wales, Dame Nicole Jacobs, shared information on how to opt out on social media.
Emma Pickering, Head of Technology-Facilitated Abuse and Economic Empowerment at the domestic violence 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.
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"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.
"Most survivors we support now have experienced some form of technology-facilitated abuse. To meet rising demand, Refuge set up a specialist technology-facilitated abuse and economic empowerment service in 2017, the only one of its kind in England.
"Abuse doesn't happen because of an emergency alert, but we know that the widespread use of this system may be incredibly worrying for survivors with a hidden device."