You are buying 1x Self- illuminating Tritium Glow Marker
This is a glass vile filled with Tritium Gas, the gas lights up the phosphorus on the glass giving off a glow that will last for 10 years. They do not require batteries or recharging to make it glow & will remain constantly illuminated even during prolonged periods of darkness.

Don’t worry about the radioactive gas inside. The keyring does not give off any radiation, and if the gas was to somehow escape the beata radiation is unable to penetrate your skin and would quickly dissipate.
Typical applications
Attach to your keychain so you don’t lose your keys in the dark
Mark the position of you tent or sleeping bag zip for fast orientation and exit.
Attach to a Maglite or other torch for easy location in the dark
A unique item to give as a gift for the person that has everything

Features:
Glows Continuously For 10+ Years!
Manufacture date September 2011
Will Work Under Water
No Battery, No Switch... its Always On
Wire Screw-Clip For Fast, Flexible Attachment
Unbreakable with normal use Polycarbonate Case
Brand New & with packaging

Specifications:
Length - 40mm
Diameter - 10mm
Wire ring - 35mm

Choose the colour you want after winning Blue - Visible from 20m away
Green - Visible from 30m away

It gives off about the same glow as freshly charged glow in the dark paint used on watches.
Green is 30% brighter than blue