Tritium is commonly used in gun sights, watches, and in exit signs.
Some rifles use tritium in their gun sights. Around 12 mCi is the common amount. This tritium is dissolved in a phosphor liquid in a glass vial.
Another use of tritium is in watches. Tritium is commonly used in glow-in-the-dark watches, useful for people who work in dark environments for long periods of time. While it isn't the brightest (a product called Superluminova is brighter), tritium doesn't need an ambient light source to charge itself. It also glows consistently at the same brightness, providing unlimited readability.
Lastly, several curies of tritium is used in exit signs, used for when a fire breaks out in a building.
SAFETY DISCLAIMER: While tritium is a fairly low-risk item, it is still hazardous and using it has certain risks. Using gloves, having proper ventilation, and disposing of used or damaged tritium objects greatly decrease those risks.
Included below is a webpage that talks more about tritium and another webpage that shows some cool tritium watches: