In the world of Bluetooth hands-free kits, it's somewhat difficult to make an impression. A lot of the devices are very similar, so companies have to focus on usability and design to really create a product that stands out. Plantronics Discovery 665 is the company's latest attempt at this, and it's quite a nifty little unit. Unlike most of the other hands-free kits on the market, the Discovery 665 doesn't have an ear clip, instead, the unit is held in place purely by a rubber ear-plug. While we're still hanging out for a model that's basically invisible, this unit goes a good way towards being less obtrusive and it should suit the mobile professional who is regularly on the road.

The best thing about this unit is its size. Measuring just 50mm x 10mm x 10mm, it's fairly tiny; much less noticeable than the chunky hands-free kits of old. It's lightweight and comfortable to wear for long periods, so you can happily leave it in during a long car or bus ride. This slim design means it doesn't need an ear hook; instead, a small rubber earpiece sits inside your ear and supports the weight of the entire unit.

It has minimal controls, with just a single control button and two volume keys. The control button does the brunt of the work, answering, ending, rejecting and muting calls depending on the length of time it is pressed for. Voice dialing is also available, along with redial, and calls can be bounced backwards and forwards between the phone and headset at any time.

During our tests, call quality was good, but not exceptional. Outgoing audio was crisp and clear with good volume and great isolation from external noise. However, incoming audio was, at times, a little soft. Changing earpieces in order to get a better fit helped a little, but the sound still wasn't as clean as some other units we've tested. Even so, incoming calls were still nicely audible.

Pairing the unit is a simple process. Just holding down the control button for a few seconds switches on the unit, and after several more seconds it kicks into pairing mode. Pairing mode is denoted by the light alternating from blue to red. It has a standard range of about 10 metres and we didn't experience any drop-outs or signal strength issues during testing.

The unit is supplied with a funky, pocket-sized, cylindrical holster. It's through this holster that the unit is charged, and it has a pocket flip on the front so that you can easily store it in your top pocket, for example, for fast access. It can charge via either a USB connection or a cigarette-lighter dongle for a car, both of which plug in to the holster. Both the USB cable and dongle are supplied in the retail package.