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I'm asking this question about an already-built world, in accordance with Are questions based on movies okay?.

One of the most famous props on the television show Doctor Who is the sonic screwdriver, which can do quite a lot. In the words of the Doctor, "It is very good at opening doors." Many of the screwdriver's other capabilities seem far-fetched, but I'm interested in that particular one: Can a device, using near-future technology, open unlock locks (for the sake of the question, a standard dead bolt) using only sound waves?

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Possibly.

Some digging led me to a project by the University of Bristol that uses sound waves to manipulate objects via "acoustic levitation". As I understand it from an early paper of theirs on the subject, they were able to create small vortices from sound waves. Associated standing waves created "traps" in which angular and linear momentum could be transferred to target objects, thus moving them in any direction.

The paper itself deals with early versions of the devices that were only used on microparticles suspended in water - not very useful for unlocking doors! However, the devices have gotten more advanced since then (see the video here), and can operate in air, while handheld. Here's a still frame from a demonstration:

enter image description here

There's obviously a huge difference between moving microparticles and moving dead bolts. However, it does seem possible that improved standing wave traps could be used to move larger objects in the near future.

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  • $\begingroup$ My friend showed me similar device he built for his Engineering PhD research. There are some pretty severe limitations to acoustic levitation. They don't use vortices, they use standing waves. The sound waves create a anti-node with lower pressure than its surroundings. The beads in the video are pushed into that anti-node. If there is a solid acoustically reflective surface between the emitter and the anti-node that surface will reflect the sound waves before they can reach the anti-node, and the anti-node will disappear. This is great for manipulating things in air, terrible inside a lock. $\endgroup$ – BobTheAverage May 3 '17 at 17:12
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You can pick the lock by jiggling some picks around inside. Whilst picking a lock is often shown in films as a delicate process of bumping up each pin individually you can use the much less elegant bumping method.

“Bumping” is a lock-picking technique that refers to the repeated striking motion used to dislodge the pins inside a lock.

(Basically just jiggling the the pins up and down and putting a little pressure on the barrel at the same time to make them stick if they get into the right place).

Now we just need to hit the resonant frequency of the air in order to drive air into the cavity inside the lock and push the pins up. The now bouncing pins will act as if you're bumping them and you can use the normal technique.

You will, however, need to turn the barrel at the same time and although it isn't the standard approach in Doctor Who, you could still do it.

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