Higher Voltage = Improved Signal Strength
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Filter capacitor on input.

Try adding a 100 nF capacitor on the input to your micro. This will shunt any high-frequency noise to ground and provide a little "debounce". The small delay when the switch opens - a couple of milliseconds - should not delay you getting the car in and out of the garage.