Wow, one of my posts got referenced in another conversation!
That wireless pyrotechnic igniter looks pretty slick, and it's considerably cheaper than the homebuilt system I'd described for doing the same job (passing a coded signal over a radio link to arm, and another coded signal to launch). You might be able to say that the keyfob is
the safety key, since the system cannot be armed & launched when it is removed. It's kind of iffy though.
If you really wanted to you could do it with IR, but potential problems include:
a) bright sunlight, the type that's often present on good rocket launching days, may interfere with the signal getting through
b) if your system is looking for a simple flash of IR, it could be triggered by sunlight, a backfiring car, the glint off a pair of sunglasses... a system looking for a coded signal will have the same design & cost problems as a radio link
c) the reciever will have to be mounted on a structure to keep it above the grass, since a single blade of grass could block the signal
d) you'll have to clean the reciever's lens thoroughly after every flight, since it'll get coated in rocket exhaust gunk
For the price you would pay for any wireless launch system -- radio or IR, homebrew or commercial -- you could buy a spool of wire, a nice rocket kit, and a whole bunch of motors. A wireless launch system could be very cool if designed and built safely, and rocketry is all about cool, but a rocket and a pile of motors is cooler than a wireless launcher.
On a related subject...
A friend of mine insists that a powerful radio control airplane transmitter is capable of setting off an Estes igniter that's attached to a WIRED launch system. I can almost believe it, if the launch leads were exactly the right length to act as an antenna, but it seems real unlikely. My plan to prove/disprove this involves launch leads cut to a length matched for the frequency I'd broadcast, a CB radio, and an HF amplifier several times more powerful than any R/C airplane pilot has ever used.