Optical Flow systems maybe somewhat more complicated and difficult to use than, sonar or sound, they may also add additional weight and therefore increase size and you could lose your advantage in that case depending on your mission. The reason I bring up these matters of how to fool a MAV or defeat one, or kill it, so to speak, since it will be behaving more similarly to an organic machine than a simple devise. Well because the academia crowd is sharing information with other countries.
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These MAVs after all are a combination of many sciences, many of which are life based, which are not very secret in that anyone can sit out side and watch a Bee fly in a zigzag pattern like you have to do when you taxi a tail dragger so you can see where you are going and what is coming up. Now then is an optical sensor really the best bet? Some of the best and brightest agree that it is. However Bats do not crash into things and they use sonar, or do they really use both optic flow sensors (it's brain and eyes) with the benefit of sonar too? Well at least we know they always turn left when they exit a cave? Interesting.

Learn everything you need to know about safety sensors for garage door openers. We'll talk about definitions, why they're important, how to replace defective or damaged sensors, and why you can't bypass them.
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There are two safety sensors in a garage door opener system. The first is located on the receiver, while the second is located on the transmitter. You can easily tell them apart by looking at the connector cables. The receiver will have a black and white cable, and the transmitter has a solid white cable.

The door will always open, regardless of whether the sensors are working or not. However, for the door to close, the sensors must be both connected and working properly.

Why sensors are important

Because sensors tell the garage opener to open or close, they are important components of the system. They are primarily included to protect small children from getting crushed under the weight of the door. However, they are useful for a variety of reasons and situations like:

protecting animals from injury
preventing damage to user's car
stopping the user from damaging the door

How to replace defective or damaged parts

While it is possible to repair these parts yourself, most people choose to replace them. When purchased, most come with brackets and a limited manufacturer warranty.
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Assembled, the sensors are approximately 3 x 10 x 9 inches, and weigh an average of two pounds. They are typically sold in pairs for around $40. To replace the defective or damaged parts, you'll need to locate the two sensors.