Free Speccy Spectrum Analyzer

Turn your phone into a Spectrum Analyzer. Speccy is an Audio Spectrum Analysis tool, which visualizes the spread of sound frequencies in the audible (and inaudible) spectrum, detected through your device's microphone, using Fast Fourier Transform signal processing. It supports the most languages of any similar app (English, Spanish, Portuguese, Polish, German, Italian, Russian, French and Thai - with more languages added regularly) and is the only app on the market which also lets you export audio snapshot data to the clipboard (for plotting in Excel, etc).
Speccy has a wide variety of uses, such as:
• Assessing environmental noise for health and safety
• Sound checking venues PA systems and in-car stereos
• Identifying audio signals obscured to the human ear by noise
• Testing the microphone on your device
• Comparing the quality of different brands of headphones
• Testing signal generators
• Tuning musical instruments
• Measuring audio signals just outside human perception. As people age over 20 years, their aural perception range drops well below 21 kHz
Speccy has been used successfully to find gas leaks, test ultrasonic pest control equipment and has even used by EVP enthusiasts to try and detect ghosts!
The app could also help you get into a safe with a mechanical combination lock for which you have forgotten the code: With your device acoustically coupled to the safe's dial, turn the dial slowly, you can 'hear' when a tumbler drops in, because the spectrum of the sound will be very slightly different than turning one 'normal' tick (depending on the build quality of the safe). Using this technique you can detect when you hit a correct number and start dialling the other way.