A good portion of my adolescence was devoted to re-creating "Star Trek" props from household items. I still have my Lego flip communicator.
Now I can save myself a lot of time, effort, and Legos by dropping $30 on ThinkGeek's Star Trek Electronic Door Chime.
A DIY "Star Trek" door can be done. This guy made one. If you don't have the patience for that kind of elaborate project, you can settle for the ThinkGeek door chime's swooshing sound effects instead.
A motion sensor sets off the swoosh when a crew member crosses the threshold.
If the soothing door sound isn't enough to get your attention, you can set it to red alert. You will have to provide your own battle station.
The chime looks like one of the wall communicators from the original series and runs on six AA batteries.
The only safety precaution I would recommend is to not wear a red shirt when in the vicinity of the chime.