Anyone know of where you can get one of theses in Bangkok or surrounding area ?

I would be interested in that also.

Do these pens work for all currencies or just for a specific one?

You can buy them on Amazon.

http://www.amazon.co.uk/s/ref=nb_sb_noss_2/275-5596902-2092507?url=search-alias%3Daps&field-keywords=pen+for+checking+currency

I've had several 100's with the pen mark on it be rejected from Bangkok Bank....just because there was a mark on it.

I bought some a year back from 7-11. The colour from the pen fades without trace after a short while. Another alternative would be to use a black light pen similar to a laser pen.

I bought some a year back from 7-11. The colour from the pen fades without trace after a short while. Another alternative would be to use a black light pen similar to a laser pen.

Short Wave or Long Wave? (serious question)