A tennis ball on a string may good at letting you know when you've fully pulled your car into your garage, but it can get in the way, plus its location is based on the length of one specific vehicle. Inventor Mitchel Ottinger has created what he thinks is a better system, in the form of Park-a-Dot.
Since the early 90s, all garage door openers have been required to be equipped with safety systems that keep the door from closing on obstacles. These systems consist of a unit that emits a beam of infrared light, along with a sensor that receives that beam. If that light is blocked by something in the path of the door – such as a car or a person – the beam won't be received by the sensor, and the door will stop closing.
Park-a-Dot works with such systems, sensing that infrared beam. When the car's bumper is clear of the door and the beam is no longer blocked, Park-a-Dot projects a red dot of laser light onto the garage wall in front of the vehicle. This lets the driver know that they're far enough in, and they can stop.
It can reportedly be user-installed in about 20 minutes, and is powered by two AA batteries that should last for over a year. It should be noted, however, that the system will only work with garage door openers made by Chamberlain, Craftsman or LiftMaster.
If you're interested, Park-a-Dot is currently the subject of a Kickstarter campaign. A pledge of US$29 will get you a setup, assuming it reaches production. The planned retail price is $40.
The system is demonstrated in the following video.
Source: Kickstarter