If you can change your voicemail, you can call for help

A tip goes round: before you lose signal, change your voicemail greeting to say where you are. If your phone dies, anyone who rings it will hear where to find you.

It sounds clever. It has a flaw that can waste the two things you may have least of, signal and battery.

If you are in trouble and your phone has any signal, call 911 (US) or 999 (UK) first; a voicemail greeting needs that same signal and may never be heard.

This page is for a phone that still has some signal. If you have none at all, the last section says what it cannot tell you. If your phone says “No service”, try 911 or 999 anyway: the UK government says emergency calls on a mobile use any available network, and US carriers must pass on every 911 call. If someone is hurt, stop reading and make the call.

Why the greeting does not do the job

Some people point out that a voicemail greeting is normally kept by the phone company, not on your phone. To change it, your phone has to reach the phone company, and that takes a connection.

Some people draw the same conclusion from it: a signal good enough to change the greeting is good enough to call for help or send a message directly. A call goes to someone whose job is to act on it. A greeting waits for somebody to ring you, listen to it and decide what to do.

One person says friends and family tend to text rather than ring, so a greeting may never reach them; another person adds that their dentist would be the one to hear it.

Some people defend the greeting as a back-up for one narrow case: the phone dies after you set it and before you can call. One person suggests an order, call first and change the greeting afterwards, in case the call drops. If a call does drop, the call-taker may try to ring you back, and the FCC says to be ready to give your number so they can. Keep the phone on and free.

What to do when you have a little signal

1. Call 911 in the US or 999 in the UK. In the UK, 112 also works from a mobile. Elsewhere, use your local emergency number.
2. Say where you are first, answer the questions, and stay on the line until the call-taker tells you to hang up. There is a page here called Say where you are first about what to say.
3. If the call will not connect, move a short distance and try again. The UK government says emergency calls on a mobile automatically use any available network, and that moving a short distance can sometimes improve signal. In the US, FCC rules say carriers must pass on all 911 calls, even from people who are not their customers. The FCC says to wait about ten seconds before you redial. Some people also suggest switching airplane mode on and then off, which makes the phone search for a network again.
4. If calls will not go through but a text might, text someone you trust. Say where you are and what is wrong, and ask them to call 911 or 999 for you. Whether you can text 911 or 999 itself is covered in the next part. The FCC says text messages will go through in many cases when a call may not. FEMA says texts are more likely to get through when a network is overloaded. The UK government says messaging may work even when calls do not. Some people give the reason: a text needs only a short connection and can wait until the signal comes back. Those agencies write about busy or damaged networks, and this page found none that says the same for a single bar of signal.
5. Send a plain text message to a phone number, not a message in an app. The FCC says messaging apps that only message other users of the same app are not required to support texting 911, and some people say app messages need internet data.
6. Use the phone sparingly. The UK government says to use devices sparingly to save battery until you can charge them again.

Texting 911 or 999 itself

In the US, 911.gov says it is always best to call 911 if you can, and text if you can’t. Texting 911 is only available in certain places. Where it is not, your phone company must send back a message saying the text was not delivered; if you see that, call, or find another way. The FCC publishes a list of the areas that take texts. If you are deaf, hard of hearing or speech-disabled and texting 911 is not available, the FCC says to use a TTY or a telecommunications relay service if you can.

In the UK, you can text 999 only if you registered first. The service is for people who are deaf, hard of hearing or speech-impaired. To register, text “register” to 999 and follow what comes back: one fire and rescue service says you then text back “Yes” and get a message confirming it. Do it now, not in an emergency. In an emergency, text 999 and say who you need (police, ambulance, fire and rescue or coastguard), what the problem is, and exactly where. Do not assume the message arrived until the service texts back. It can take about two minutes. If nothing has come back in three minutes, try again or find another way. Mountain Rescue England and Wales, a charity, also says to start with the word “Police”, then give the details and where you are, and to charge your phone before you set out. After you call or text, it says to stay where you are until the rescue team contacts you.

If you are in danger from someone near you and cannot speak, on a mobile in the UK: dial 999, listen to the questions, cough or tap if you can, and press 55 when the recorded message asks. The Independent Office for Police Conduct’s guide says that staying silent without pressing 55 ends the call, and that pressing 55 does not tell the police where you are, so answer their yes-or-no questions by tapping or coughing if you can.

Before you go where the signal is poor

Tell one person where you are going, what route you will take, when you expect to be back, and what to do if you are late. Mountain Rescue England and Wales says to leave your start and finish points, your expected time back and your contact details in a reliable place. If you go alone, it says to tell people your route and when you expect to finish, to stick to it as far as you can, and to say so if your plans change. Some people suggest the same.

Some people suggest regular check-ins instead of a one-off greeting: trip details in a family group chat, or scheduled check-ins from a satellite device. One person suggests texting a contact the route, where the vehicle is and when you expect to be back, then texting again on arrival and again on getting back to the vehicle, so that searchers have a timeline. One person says that in popular walking areas of the UK you can leave a route card and a contact number at a hotel, visitor centre or post office, so that someone there can alert the emergency services if you do not return.

Charge your phone first. Mountain Rescue England and Wales says many accidents happen late in the day, when both you and your phone are low on energy. Some people suggest carrying a power bank, and one person suggests a car charger and cable for the phone you already have. The UK government says GPS may still work with no signal, but map apps need maps you downloaded beforehand; there is a page here called Download the map while you still have signal. It also says to keep a paper copy of important numbers; there is a page here called Write down the numbers your phone remembers for you.

For regular trips far from any coverage, some people point to a satellite messenger or a personal locator beacon, and one person says some national parks lend beacons. This page does not compare costs or models. A beacon calls out a rescue team, so it is for real emergencies.

A spare old phone in the car or at home

Many people suggest keeping an old phone charged in the car or at home, because a phone with no plan can still dial emergency numbers. Three checks first.

First, a phone with no plan gives no location. In the US, 911.gov says all wireless phones, even those with no plan, can call 911. The call does not give the call-taker your location, and they cannot call you back. So say where you are straight away. If you are cut off, the FCC says to call again yourself. Some people say that whether a phone with no SIM card can reach emergency numbers differs by country. This page could not confirm at an official source whether a UK phone with no SIM card can call 999, and one person says a SIM is required there, so do not count on it.

Second, old networks are being switched off. The FCC’s guide to the US 3G shutdown, now archived, says many older phones cannot make or receive calls and texts, including calls to 911: 3G phones, and certain older 4G phones that cannot make calls over the 4G network (VoLTE). Some people warn the same about the 2G and 3G networks where they live, and Ofcom, the UK regulator, has a page on the switch-off of the UK’s 2G and 3G networks. Ask your phone company whether an old phone still connects where you live before you rely on it.

Third, a hot or freezing car is a poor home for it. The US Fire Administration says not to keep lithium-ion batteries, the kind in phones, in direct sunlight or hot cars, because that is a fire risk. It says to store them at room temperature when you can and not to charge them below 0 °C (32 °F) or above 40 °C (105 °F). A UK fire service says high temperatures speed up battery ageing and make failure more likely. Some people warn that a cold battery loses charge fast, which makes a phone left in an unattended car a risky back-up. So keep a spare phone indoors or in your bag with a power bank, and check its charge now and then. If a battery gets too hot, changes shape or colour, leaks, smells or makes odd noises, stop using it. If a battery catches fire, the US Fire Administration says not to try to put it out: get out and call 911 (999 in the UK).

Who this page is not for

With no signal and a flat battery, this page cannot help; what to do then is not covered here. If you are stuck in a car in snow, there is a page here called Dig out the tailpipe before you run the heater.

If the danger is a person near you and you cannot speak, the 55 line above is for UK mobiles, and Say where you are first covers more.

If you are deaf, hard of hearing or speech-impaired, register for the UK text service now; Relay UK can also connect you to 999 on 18000. In the US, check the FCC list for your area, and have a relay service as a second route.

Outside the US and the UK, the numbers differ, and this page does not list them. And if your trouble is weak signal at home, not a trip, that is a different problem and not covered here.

If you are in danger now, call 911 in the US or 999 in the UK.