I think what you are referring to is a small flash which sits on the camera but it has a filter in front of it so it only emits infra red light which will trigger ordinary light operated flash slave triggers.
If so, an easier method is to put a deep red filter in front of your camera's inbuilt flash. A piece of theatre lighting gel (or many layers of red and purple wrappers from Quality Street) would do it.
It would still put out a bit of visible light but with a deep enough filter, I don't think you would see it in the image.
Steve.
Boringly, he's right again
But IR triggers only work with a good line-of-sight and turning your camera slightly away from the flash you want to trigger will mean it won't see the signal and it won't fire
They work well in studios though, providing there isn't lots of window light and again there's either line-of-sight or the studio is small enough for the signal to bounce around plenty and trigger the remote flash from anywhere
They also don't work where it's already very bright - i.e. outside or even in such as a conservatory
Basically, normal studio = ok - anywhere else =
Which is why radio triggers are more common, useful & reliable
I use Skyports, they have been 100% reliable and work up to 100 yards (more than enough IMO); Pocket Wizards are the 'industry standard', and come with a remortgage to pay for them

; then there's the Fleabay ones, which may or may not work at all let alone reliably - some report good things, I paid £50 for a set and literally threw them away in frustration
HTH
DD