This is a really good quality source of real UV light (not just a violet bulb), that is compact enough to sit amongst your bunch of keys, & reliable enough to use in counterfeit money detection, many UV torches have enough UV to make neon cosmetics glow in the dark but few have the ability for real detection purposes such as picking up Smartwater or the marks on passports, driving licences, & credit cards. Non replaceable batteries included 5cm diameter x 1cm depth UV Counterfeit Keyring Torch