Every time we test portable music players or mobile phones, we end up saying the same thing: the headphones that are supplied aren't up to the job.  There isn't a single exception, and replacing them is a good idea if you have an entry-level MP3 player--and absolutely essential if you shelled out for a more advanced device.

The market for headphones for portable devices is divided into three different segments: traditional headphones, more lightweight versions and finally in-ear headphones, that we're looking at here.

What are in-hear headphones?  What's the difference between them and traditional headphones?

Unlike standard headphones, in-ear headphones slide into your ear canal.  They're perfectly safe, as long you keep your ears clean.  Depending on how far you push them in, there is sometimes a distinction between semi-in-ear headphones and in-ear headphones, but the difference between the two is often limited.  The basic principle is the same as for any device producing sound: an electric current induces movement, which in turn produces vibrations in the air; changing the electrical signal changes the sound that is produced.

In-ear headphones: the pros

As we said before, in-ear headphones go right inside your ear, and they're covered in silicon or rubber, or else tipped with foam.  That means they are much better at isolating you from external noise than other types of headphones.  Only those headphones that use active noise reduction can rival them, but they're much larger and often produce a gentle hum while they work.

Once you've put them in, you're totally cut off from other sounds around you.  You can quickly get used to not having to listen to the chatter of those around you on the bus or the tube slamming on its brakes.  You can use this to your advantage by playing your music at a lower volume, protecting your ears.

In-ear headphones: the cons

This excellent isolation also causes problems precisely because you are cut off from the world around you.  It can be dangerous to use them while you're out and about, and if you're cycling or skating you'll hear almost nothing.  You're much more likely to run into another vehicle--and that's going to hurt!  The same is true if you're out walking or jogging: it's all too easy to find yourselves surprised by a car or a motorbike as you cross a street.

You don't always realise it, but your ears are a valuable source of information, especially in urban areas. So be careful!

Finally, remember that not everybody finds the sensation of having headphones inside their eye particularly pleasant.  Try them out before you buy.