These are small and surprisingly bright units that you can more or less mount anywhere you like.
They are perfect for keeping in your bag, desk drawer or saddle-pack, so if your main lights run down you can stick these on and be seen. The rear is brighter and features a CR2032 battery, with the front slightly dimmer and running on two CR2016 batteries. The run times, as you would expect due to the battery differences, are much longer on the rear.
The Backupz are not designed to be used as main lighting but theyre prefect for keeping handy for those 'just in case' moments as the batteries will last a long time when the lights are not in use.