Last October, Altec Lansing's inMotion speaker system became one of the first, and certainly the most notable, of a group of high-tech accessories specifically made for the iPod. The two-speaker dock turned an iPod into a stereo, and could charge the iPod and sync with iTunes; it was an immediate hit.

Now the company is shipping not one, but two successors to the inMotion: the inMotion iM3, compatible with all iPods, and the inMotion iMmini, which, as its name implies, is compatible with only the iPod mini. The new models will be available in January and will cost around £130 and £100 respectively.

Both the iM3 and the iMmini provide the same basic functionality of the original inMotion. When collapsed for travel, each is approximately the size of a paperback book. Both provide a dock connector – the iM3 via a dock-like slot, the iMmini via a small "shelf" – that feeds audio to the speakers and also charges the iPod when using the included AC adapter.

In addition, when you connect the iM3 or iMmini to your computer via your iPod's dock connector cable, you can sync your iPod with iTunes whenever the iPod is "docked" with the speakers. Finally, a 1/8" auxiliary input jack on the back of each system allows you to connect a first- or second-generation iPod or any other audio source (such as your computer or another portable audio player).

Power and battery life are also consistent with the original inMotion, as the new systems provide 4 Watts of total power and are expected to play for up to 24 hours, depending on volume levels, on four AA batteries. An auto-shutdown feature automatically turns the systems off when your iPod is removed or stops playing for more than a few minutes.