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If you want to know where friends and family are (but don't necessarily trust them to tell the truth). then try Apple's free Find My Friends app (apple.co/Find). Your contacts can opt into having their location revealed on your phone. which is useful for organising nights out and tracking people who are prone to wander off. but not so good if you're planning a surprise for someone or are having an extra-marital affair.

For something a bit mor sophisticated try Glympse (www.glympse.com) which offers timed ‘gllmpses' of someone's location and is able to estimate how long it'll take them to reach you. based on their current progress. It's available for Android. iOS and Windows Phone.