Echo

Continuously record audio for retrieval at a later time.

Unless saved, recordings are deleted on a rolling basis.

record harassment and bullying (even when you didn't anticipated them)

save important pieces of information (phone numbers / passwords / instructions)

record cute/funny moments

prove that someone said (or didn't say) something

Limitations

The app employs a range of tricks to reduce battery usage but it's still draining quite a bit.

You'll have to check your device to see how it affects your battery.

Battery drain is comparable to having constant audio playback.