While the most obvious use case is for being woken up the manufacturers suggest it might also be useful for reminders about regular events such as taking medication, or going out on the school run.
In operation the ZBand is very simple. When an alarm goes off it can be cancelled by holding down the central "Z" button on the band for 3 seconds. Alternatively a single touch will put the alarm to sleep for the user specified period.
The ZBand Windows Phone app has a simple interface, with alarms and related settings saved to the ZBand over Bluetooth (you'll need to pair the ZBand with your phone before using the app). Once an alarm has been set the ZBand operates independently of your Windows Phone device (i.e. it is not always connected), which helps ensure reasonable battery life (roughly 10 days on a 30 minutes charge). Apps for Windows and Android are also available.
The ZBand is the product of an Irish based start-up and is now available for purchase through the ZBand website at a price of €39.99 (£32 / $50), with worldwide shipping included. That's a very reasonable price for a wearable accessory, although it fair to say more expensive smart watches do include ZBand's functionality as part of their feature set. However, aside from being more affordable, there's a definite benefit to a simple approach, both in terms of ease of use and design comfort (ZBand is significantly smaller and lighter than a smartwatch).