The reason why you can find these modules is because 434MHz is an ISM band in some parts of ITU Region 1. You won't find an garage door opener there in the US. In the US you should use the 315MHz version which allows for license free use.
While 434MHz is in the 70cm amateur band you really should have an ID coming out of this thing when it transmits. All you need to do is shove your call sign out at 20wpm Morse code at the end of your transmission.
There are some comments on the SparkFun page suggesting these transmitters are "Part 15" compliant (or at least can be, if only transmitting intermittently): https://www.sparkfun.com/products/retired/8946
Thanks for letting me know. I made sure the ATtiny84s could be re-flashed in circuit in case something like this came up. (I also have 315MHz modules, and will prefer those in the future. Swapping out the transmitters and receivers will only take a bit of resoldering.)
Actually, according to the ARRL band map, 434MHz is for repeater links, so even with a license you really shouldn't use it for this kind of stuff, unless it is below the "intermittent" limits on that FCC link.
While 434MHz is in the 70cm amateur band you really should have an ID coming out of this thing when it transmits. All you need to do is shove your call sign out at 20wpm Morse code at the end of your transmission.
Otherwise it's a cool little hack.