Streamlight Stylus
The Stylus is a pen-shaped flashlight by Streamlight. Among the many penlights in the market the stylus has the distictive advantage of being one of the thinnest versions being as thin as a regular ball pen or a mechanical pencil, other products are bulky when compared to a pen.
The stylus has a button on the tailcap for momentary activation, you can also tighten the end cap for constant on mode when needed in a penlight momentary use is probably the most used mode so the button is very useful.
The light uses three AAAA (that is four As) batteries, not very common to find but not hard or impossible, the AAAA batteries have the same length as AA or AAA batteries but are thinner. Some models of 9v batteries are made of 6 AAAA batteries so in case of emergencies you can "attack" a 9v battery to get the AAAAs.
The beam is dim as expeced from the regular 5mm led in this light but useful as a small task light or for quick inspections, it has a long runtime of more than 50 hours. The total brightness for the white led version is 10 lumen. The pocket clip is more oriented to a shirt than a pocket because it is rather small, so it can be seen as the regular clip you can find in a pen.
The light is available in white, red, blue, green and UV LED colors and several body colors to choose. You can read more about it at streamlight website or order from EDCdepot for $14.