If you've just completed a three-hour bike ride and an hour's drive home, it's entirely possible that once you're finally pulling up into your driveway, the fact that your bike is mounted on the roof of your car might not be the first thing on your mind. If you don't have a garage, that's no big deal, but if you do ... well, you could just proceed to drive into it out of habit, and end up smashing your bike against the bottom of its raised door. That's what cyclist Tom Reiber did on one memorable occasion, and it prompted him to invent the HeadsUp wireless gear alert system.
HeadsUp consists of an LED alert sign/control module that mounts in the garage, a small wireless water-resistant tag that stays on one's bike or other car-topped gear, and an auditory alert unit that mounts inside the vehicle. As the driver approaches their garage, the garage-based module detects the tag, and lights up with a visual warning. At the same time, the car-based alerter sounds a tone, both units reminding the driver not to enter the garage before taking their bike off their roof rack.
The system comes with two tags, each of which can be permanently left attached to different bikes, kayaks or other items. Those tags can be transferred to other objects as needed, or users can order additional tags (along with additional in-car alerters). The control module, which runs off mains power, displays a visual warning when it detects that a tag's battery is getting low - something that should reportedly only occur about once a year.
A complete HeadsUp system can be preordered from the company website for US$169.99, and should ship early next month.
Of course, you could also simply leave a reminder for yourself, such as a trash can in front of the garage door. In the same way that you could forget about your roof-mounted bike, however, you could also forget to leave yourself that reminder.
Sorry - I think the suspended bar system or a rope and tin cans or something, before the garage door is much easier to use.
Something like this:
http://www.holeintheclouds.net/sites/default/files/good_morning/10oct/ifyouhit.jpg
@nbs - I agree - having almost got stuck in a multi-storey car park with a Land Rover brings this home painfully...
A general system could be useful for over-height lorries on motorways etc which have a habit of clipping bridges on rare but regular occasions.