Misconstruction without equal, albeit bright

The lamp would be good: it is light, has a robust housing and the right size for the keychain. If she had not constructed fundamentally wrong:
At the lamp head can unscrew the lamp to change the battery. This thread makes it the light and on / off. Ie there is no real power button. If the lamp is off, the thread is always half psyched up. If you rotate one revolution further, the head is off. Thus, it is no longer watertight, and eventually flies off the whole lamp head. So you have only a shaky thread to turn off the lamp. In addition, the beam does not focus, so you have only one means good compromise between range and scattering.

The perfect flashlight for the keyring is not this rickety structure.