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Demystifying 999 calls on a mobile phone

Over the many years we have heard it all…….

I can always make a 999 call – even when there’s no signal

A mobile phone will make an emergency call without a SIM card

There is a special number which is pre-programmed into every SIM card that will dial 999 when there is no signal

and many more.

We’re big fans of myth busting so here are the FACTS about mobile phones:

can i make a 999 call without a signal?

The most common myth is that you can make a 999 call when there is no signal. Well, depending on your definition of ‘signal’, this is partly true.

For simplicity let’s say that a ‘signal’ is what the phone uses to communicate with a ‘cell’ (mobile phone network mast). This uses small radio waves and, like all radio waves there must be a clear line-of-sight for the phone to connect to a cell which, if all is well and good, allows the phone to be in ‘service’.

However, If something blocks the signal, (such as a mountain or large brick wall) the signal may not reach the cell. In many instances this is not a big problem as there are usually several cells in any given area which offers a greater probability of making a connection. However there are times when there is no signal and therefore no calls can be made i.e. in a tunnel, deep valley or remote location. The phone now has ‘no service’ available on any network – here in Cumbria this is very typical!

MAKING A 999 CALL on another network

In 2009 all mobile phone network providers introduced the ability to make cross-network emergency calls. This allows anyone to make a 999 call on another network should their own network (home network) be unavailable. For example if you subscribe to O2 but there is no O2 network available where you are calling from the phone will search for any other available network in your vicinity and, once it finds another network (i.e. Vodaphone), it will allow you to make a 999 call using that network.  This is technically called being camped-on, and is free in the UK (and many other countries).

When A MOBILE PHONE cannot make a 999 call

Another common myth is that it is possible to make a 999 call on a phone without a SIM card. This would be handy however phones without a SIM card are blocked from making any calls to reduce the frequency of hoax calls.  This has often confused people as a SIM-less phone may display ‘Emergency Calls Only’, however that is just the phone’s software displaying the message when turned on. As the phone is not yet subscribed to any network it will not be possible to make a 999 call.

It is possible, however to make a 999 call on a Pay as you Go phone with no credit left – good to know!


Going back to our original myth that it is possible to make a 999 call when there is no signal it is perhaps worth understanding each stage your phone goes through in it’s attempt to make a 999 call.

1.  To make a 999 call the phone needs to show some ‘signal bars’ or a message such as ‘emergency calls only’.  It must also have an active SIM card (with or without credit).

2. If your home network is available your phone will connect to the emergency services on this network. This also has the added advantage in that they can call you back should you break the connection  or if they require further details.

3. If your network is unavailable but a signal is available on another network your phone will use this alternative network to connect to the emergency services. This is technically called being camped-on, and is free in the UK (and many other countries).

4. If there is no other network available you will not be able to make a 999 call.

RECEIVING  CALLS in an emergency

In most circumstances making a 999 call on a mobile phone will simply require a signal and, once the emergency dispatcher has recorded all the necessary information, the ball starts rolling to summon emergency help. The emergency dispatcher will stay on the phone if they deem it necessary to i.e. to talk the caller through how to carry out CPR. In remote outdoor settings calls should be placed to the police who will pass all the necessary information about your emergency to a rescue team in your locality. It is quite typical that the rescue team will call you back to gather further information, particularly about your location.

It is important to note that when a phone that’s not using their home network  (camped-on) can only place a 999 call. They cannot receive a call back on that network, even if the inbound call is from the emergency services.

So if the emergency services needed to call you back (i.e. to update their progress or to gather further information about your location) they will be unable to do so unless you are connected to your home network. This may not seem that vital if you are in an urban setting when an ambulance is only 20 minutes away (if you are lucky!) however this would be incredibly significant in a remote settings where the use of search & rescue teams may be the only option of rescue and a two-way conversation will be more important – good to know! 


It’s possible to text the emergency services if you have poor signal, hard of hearing or need to make a ‘silent call’. More in this blog >>

You can make a 999 call from any phone that has a password lock. Simply dial 999 or look for the word ‘Emergency’ which will open a new screen to make the 999 call from.

Many smart phones now have a ‘Medical ID’ app which can allow a rescuer to gather further information should you be incapacitated. More in this blog >>

You can use a smart phone to pinpoint your location without any signal or data connection anywhere in the world. More in this blog >>

Written by Ross Wallace, Senior Trainer