A new app for iOS will allow you to record what you've heard - in the past.
Despite being billed as a "powerful time-shifting app" and sounding like it's powered by witchcraft the app - called 'Heard' - works on quite a simple premise.
When switched on the app starts recording via the phone's microphone onto a buffered loop.
If you hear something you want to record you simply go into the app and press save.
A free version of the app allows for 12 seconds recording - meaning you'll probably have to shell out a pretty reasonable £1.49 for the paid version which allows for a much more useful five minutes of buffer.
Quite what nefarious uses you use the app for is up to you but it's a quirky little tool if nothing else....