Every mobile phone has a unique 15 digit code called an IMEI number, short for International Mobile Equipment Identity. You can use this number to track a lost phone and you can even wipe data off a lost phone if you have this number!
You might need to find your IMEI number if you want to unlock your device to use with other networks, or for some insurance policies.
You can find your IMEI in the following ways:
By entering *#06# on your phone's call screen
For Apple devices go to https://support.apple.com/en-gb/HT204073 for details of how and where to find the number
Some other phones will allow you to find the number in the settings menu
Make a note of this number and keep it safe!
Can be used to track a lost phone
You can wipe data off a lost phone if you have this number. You call your provider and give them the number and they can then instigate a trace and/or wipe the data on that phone remotely.
You will also need this number in order to get your phone unlocked and did you know that at the end of a contract the company you had that contract with has to unlock your phone when you ask and it should be free!
For more information about IMEI take a look at https://en.wikipedia.org/wiki/International_Mobile_Equipment_Identity