Smartphones have way more features than you probably use. But they can do even more than you think. App designers have figured out some creative uses you won't believe.
Heard for iPhone is always recording using your smartphone's microphone. At any time, you can save audio from up to 5 minutes in the past.
Awareness for Android and iPhone uses your smartphone's microphone to keep track of noise around you while you're listening to music. Any sounds louder than regular background noise gets sent to your headphones.
Instant Heart Rate for iPhone and Android uses the phone's camera to figure out your heart rate. It detects the light passing through your finger and how it changes as your heart beats.
Want to go hunting for metal? Metal detector apps for Android and iPhone have you covered. They use your phone's built-in compass to find metals. You just need to hold your phone close to the ground.