Gecko

Gecko is a free, open-source time-travelling audio recorder for Android. It keeps a rolling in-memory buffer of microphone audio so you can save something that just happened, then optionally keep recording forward.

Features:
• Continuous listening into a ring buffer (foreground mic service)
• Save the last 1 / 5 / 30 minutes, 2 / 6 hours, a custom span, or everything held
• Press-and-hold a duration chip to save history and keep recording
• Settings for RAM budget and sample rate (8 / 16 / 44.1 kHz)
• Exports WAV files to Music/Gecko via MediaStore
• Restarts listening after reboot if it was left on
• Multiple UI packs (Biolume, Sonar, Oxide, Volt)

Privacy:
• No ads, no analytics, no crash reporters
• Audio stays on-device; nothing is uploaded
• Microphone is used only while listening is enabled

Battery notes:
Defaults favour clear speech (16 kHz sample rate, 256 MB buffer, power-saving mic mode, quiet notification). Drop to 8 kHz in Settings when you want quieter battery.

Source: https://github.com/anantdark/Gecko
License: GPL-3.0-only