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I purchased one that goes into the chamber like a bullet; other types are available. They work very well when doing dry-fire practice indoors. For the one I have, there is no special equipment required; no laser target, no special adapters or anything. I just "shoot" at various "targets" in the house (yes, being mindful of all safety rules). Produces a nice bright red dot on a neutral or light colored object (a little fainter but still ok on dark surfaces).
I like using it because not only is it very helpful for practice in aiming, it is also useful for trigger control training. First, I make sure the laser dot appears where I (think) I'm aiming. Then also, if I see a "streak" instead of a "dot", I know I'm moving the gun as I pull the trigger.
I've had mine for about a year. No issues. Still on the original batteries. Check it out. This one might be a little pricey, but I've found it to be very useful for me. And other types (and manufacturers and suppliers) are available that may be cheaper.
http://www.cabelas.com/product/LaserLyt ... D734095080