How can I make a garage door laser sensor?
I would recommend using laser and LDR. This will be very efficient and will not cause any problem due to light or ultrasonic deflecting. It will be precise by mm if you do thing right way. I made a simple porject back in 2005 using laser, LDR and relay. 

Here what you need to do. 

Get a laser, any laser will work. www.ebay.com/itm/6mm-650nm-DC-5V-5mW-Mini-Laser-Dot-shaped-Diode-Module-WL-Red-Copper-Head-Tube-/291089398593?pt=LH_DefaultDomain_2&amp;hash=item43c647bb41

Get a PhotoResgister www.ebay.com/itm/Reliable-Hot-New-20-PCS-Photoresistor-GL5528-LDR-Photo-Resistors-Light-Dependent-/161434780484?pt=LH_DefaultDomain_2&amp;hash=item2596434344

Put ldr in the dark box and drill a hole in it so that no other light can enter 2mm diameter hole will work. 

Connect the LRD to your board. Fire laser and change status of indicator led by the value of ldr. 

Check this link for refrence www.instructables.com/id/Arduino-Laser-Tripwire/?ALLSTEPS