Target or Flag for IR-shooting toys like the "Combat Twister" helicopter from Nine Eagles.
Unless you're playing in a complete dark room you will need an IR-filter in front of the camera. A simple solution is to add a piece of processed but unexposed film (the black part at beginning and end of a roll). Just tape it with a transparent tape in front of the camera. See screenshots for details.
Avoid aiming at windows during game and while calibrating, the sun is pretty disturbing.