This invisible ink pen (sku.88) is a funny and useful product sold at Dealextreme (and some others stores). With it, you can write hidden messages on a paper and then, when you turn on its UV light and point it to the message, it will be revealed (see the video below).
Besides the invisible ink, it contains an UV led (to reveal the written messages) and 3 (three) AG3 batteries.
Its size and weight are similar to a regular pen, so you can carry it everywhere.
Style
We acquired six invisible ink pens from Dealextreme. The only difference among them was the package (see the images above).
About the colors, it seems that Dealextreme and Focalprice sell only one color (purple). Suntekstore says that it has this item in many different colors (according to the description and images). Tinydeal sells a version of this item in red with some images on the pen, but the essential of all of them are the same (invisible ink pen with an UV light).
Price
The invisible ink pen is very cheap and can be found at Dealextreme, Focalprice, Tinydeal and Suntekstore for about $1.35. Tinydeal also sells an item pack that includes 3 invisible ink pen for about $4.4.
Build Quality
Regarding the build quality, there is not too much to comment. You just need to avoid hit the UV led, because it can stop working.
One day the invisible ink will run out, so you may think to fill it again, but the invisible ink pen is so cheap that it is worth to buy a new one than to refill the current.
Usefulness
As we mentioned, you can use it to write hidden messages on a paper, wood, skin, metal, wall, cloth and some other stuff. That is not so useful, but it can be very funny if you show it to your friends.
Another usefulness is to use the ultraviolet light (UV led) of the invisible ink pen as a counterfeit bill detector. Just turn on the UV led and point it to a bill to see some watermarks present in legitimated bills.
