Echo: Time Travelling Recorder

Echo lets you go back in time and record something after it has already happened.

★ 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 said) something



If you are having troubles with recording in other apps while Echo is running, go to and add a star. It is an issue with Android. Only way to fix this in Echo is to turn history off.


0. Is it legal to record other people?

Good question. See:

1. Why do you need these permissions?

RECEIVE_BOOT_COMPLETED - start after phone reboot
WRITE_EXTERNAL_STORAGE - save recorded wav to sdcard
RECORD_AUDIO - to record audio (of course!)

2. How does it technically work?

- it uses some memory as a cyclic recording buffer
- when it records it just points sound processor to write to this memory and goes to sleep
- when sound processor is done, it wakes, points to a next part of memory and goes to sleep again
- it doesn't process sound in any way - no resampling, no compression, it just keeps the recording going
- once you want to save recording, the memory is saved to .wav file on sdcard.

3. How does it affect battery life?

- it does affect battery less than a WiFi connection
- on my worn-out Nexus 4 it ran from 90% charge to 0% in 3 days - but other apps were also running and there was Wi-Fi and 3g turned on
- it highly depends on device and other applications - I suggest to test it yourself

4. How much memory does this use?

1/16 of total device memory but not less than 5 minutes. It's usually from 6 to 24 minutes. If you have a 2GB of RAM, it will probably store around 25 minutes. You can increase this time up to three times in settings.

5. Can it use flash memory to extend history?

It would make cpu write to flash memory. In theory it's possible but I didn't add this because it would reduce battery life.

6. Can it use free memory to extend history?

On 4.0+ devices there is a way for apps to use all of free memory and release it when system is under pressure. This however would interfere with background apps (which usually live in unused memory) and it might cause loss of recording when a memory-intensive app starts. User-controlled memory usage would probably be best but clear and intuitive design is a problem here.

KW: Microphone Recorder, Audio Recorder, Sound Recorder, Preventive, Mic., Rec., Record, Background Recorder, Voice Recorder, Best Recorder, PCM, PCM Recorder, 48kHz, Lecture Recorder, Silent Recorder, Invisible Recorder.
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Additional Information

October 28, 2014
Varies with device
Current Version
Varies with device
Requires Android
Varies with device
Content Rating
Offered By
Marek Rogalski
Cynarskiego 8 m. 1 92-447 Łódź
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