Question: **Clarification**:
I'm looking for an electrical component to use in a device that will sense large physical impacts. When an impact event occurs, all it has to do is pull one line high for around a second. There is no requirement it pull the line back down. 

I do not want this device tied to outputs from my quadcopter in any way. It needs to be standalone. I understand there are beacons with RF signals one can use for the application I describe, but that's not what I want. I just want an isolated impact sensor. :-)

I like the reed switch idea below, but was hoping for something a little more off-the-shelf. I'm going to give this a few more days before I pick one of the provided solutions.

Original Question

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I would like to know when my quadcopter impacts the ground (crashes). I am going to wire up a buzzer or other noisemaker to make it easier to find the crash site.

I've thought about using an `accelerometer` and I've thought about using a [`piezo sensor`](http://en.wikipedia.org/wiki/Piezoelectric_sensor), and I don't know which is better or if there is an even better option out there.

Requirements:

* Pull one pin high for around a second after a crash.
* Be able to survive a small crash and be useful next time around.
* Operate around 5V
* Be small (yeah, I know this is relative. Let's say smaller than 2 inches by 2 inches)
* Be lightweight (yeah, this relative too. Let's say "not heavy.")
* Less then $10 USD

So the question is: what type of impact sensor best fills my needs? I do have questions about what device to use to make a 99db sound, but that will wait for a different question. At the moment I just want a sensor that I can wire up independent of the quadcopter and have it know when a crash has occurred.

Please point me in the right direction.

Answer: 
One simple solution might be to watch an output from your receiver. For example if there is no throttle signal because you have landed the copter, then activate your sounder. You might not need an accelerometer if you can reuse a normal signal for the task. If the copter is not powered for flight, it's either on the ground or soon will be.

After seeing at the reed switch idea below, I got another idea that is a combination of mine and the reed. Place the reed switch on the motor power lead, there is likely to be enough magnetic force to actuate the reed switch. Use that to activate your sounder. Worse case you would wrap a turn of the power lead on the reed. I used this trick on an old car with a bad ignition relay, the reed wrapped on the starter lead would close to bypass the distributor voltage drop resistor. Work like a hose.. lol.
Since your goal is to find your drone once you have lost it, I would go in the autonomous beacon direction. Relying on the crashed drone battery seems a bit overconfident. Some of those key locator beacons have a pretty impressive range and would fulfill all your requirements, except for price. For instance: 

www.loc8tor.com

www.sticknfind.com