Nice iPhone app lets you acoustically measure distances of up to 25 meters

http://news.ycombinator.com/item?id=3227929 (by new user quadrix)

http://news.ycombinator.com/item?id=3221160 (by quadrix again)

http://news.ycombinator.com/item?id=3228256 (by new user greenale)

http://news.ycombinator.com/threads?id=makramer09 (new user or shill account makramer09)

http://news.ycombinator.com/threads?id=jgeorge (new user or shill account jgeorge)

http://news.ycombinator.com/threads?id=alexenko (new user or shill account alexenko)

Nice work!

Couple of thoughts:

- I only have ear phones with a mic. It wasn't immediately clear how I should measure something. Perhaps a tutorial? If I hadn't watched the video first, it would have been difficult.

- It's loud, is there a different frequency that could be used?

- Without any other background info, it leads one to think that the temperature is the only additional variable in the equation. Wouldn't it then be possible to tell the temperature with a known distance?

- Unless I have multiple iOS devices, I can only measure just past a meter (from the video). Combining this with the fact that it's not very precise, it would be much more useful if I could measure longer distances (e.g., sonar).

I realize there is a disclaimer that it may not necessarily be accurate, but it varies between 0 and some wildly innacurate value like 30 cm when I'm holding it 1 or 2cm away.

All codes are taken :-(

How accurate is this in noisy environments?

    M7TF3KPJH3WX
    KJXW974YELWX
    PE6RANNF4R6Y
    ARYLPNJY36XX
    M9EHXA694JER

1) On your iPhone/iPod/iPad, tap the App Store icon from the Home Screen.

2) Navigate to the New section on the Featured tab.

3) Scroll to the bottom of the list to locate and tap the Redeem button.

4) Enter the promo code and tap the Redeem button in the upper right.

5) Tap done on the Thank You screen, then tap the home button to return to the home screen.

6) After a second, you should see the my app installing. (If the promo code was not used before...)

7) Please upvote if you took a code and leave a comment telling which was your code (so the next person doesn't have to try in vain).

8) If all codes are used up, please reply to this comment, I will then post more. This is more efficient than posting all codes at the start.