Will BlackBox work on my phone?

What decides whether a phone can record all day

Four things, in roughly this order of importance:

The checker above scores each of these and shows you the arithmetic. Nothing about your phone leaves the browser, and no part of the score comes from a language model — it is a fixed rule set you can read in the result.

iPhone background-recording limitations

iOS lets an app keep an audio session alive in the background, which is how any recorder works with the screen off. What it does not do is give that app exclusive rights to the microphone. The microphone is allocated to one app at a time, and the system decides who gets it.

Things that interrupt an iPhone recording:

• cellular calls, FaceTime and VoIP calls like WhatsApp, Telegram, Zoom and Teams;
• Siri, including accidental wake-word triggers;
• keyboard dictation and voice typing;
• text-to-speech and read-aloud features;
• recording video with the camera;
• any other app that starts using the microphone — a voice note, a screen recording with audio, a live-captioning app;
• swiping the app away in the app switcher, or force-closing it;
• restarting the device.

After an interruption, iOS can signal that the interruption ended, but a successful resume is not guaranteed. Recording may need to be started again — which is why the honest habit is to open the recorder and check its status after any call rather than assuming it picked up where it left off. No app on the App Store can bypass this, and any app claiming otherwise is worth being sceptical about.

Low Power Mode is the other iPhone factor. It pauses Background App Refresh and reduces background activity, and it switches on by itself at 20% charge unless you decline. Charging before a session that matters removes the problem.

Android battery optimization

Android's background rules are layered, and the layers are what catch people out. From the platform outward:

1. Microphone permission — including the always-allow option where your version offers it.
2. Notification permission — Android keeps a recorder alive through a foreground service with a visible ongoing notification. Block the notification and you undermine the mechanism.
3. Per-app battery usage — set to Unrestricted. This is the single highest-value setting.
4. Battery Saver — off during long recordings, including the automatic trigger at low charge.
5. Adaptive Battery — can restrict an app you rarely bring to the foreground.
6. Manufacturer sleeping-app, deep-sleep and auto-start lists — Samsung, Xiaomi, Oppo, Vivo, Realme, OnePlus and Huawei all ship these, and step 6 is usually the decisive one.
7. Third-party cleaners, security apps and task killers — add the recorder to their allow lists.

Menu names move between Android versions and manufacturer skins, so the checklist in your result stays deliberately approximate: if a path does not match exactly, search your Settings app for the keyword. The background recording troubleshooter has the per-manufacturer paths in full, and the Samsung and Pixel pages go deeper on the two most common cases.

Storage needed for all-day recording

BlackBox records at 32 kbps AAC mono, 16 kHz — a speech-optimised setting that costs about 14.4 MB per hour. The arithmetic from there is simple:

The important idea is that retention, not daily size, decides whether you run out of space. Without automatic cleanup a library grows forever. With auto-delete after a fixed window, it reaches a ceiling and stays there: new recordings replace expired ones.

Two rules worth keeping:

• leave 15–20% of your storage free — the operating system, updates and app caches all need room, and a phone with almost no free space misbehaves in ways that have nothing to do with recording;
• plan against free space, not the size printed on the box. A 128 GB phone with 4 GB free is a 4 GB phone for this purpose.

The audio storage calculator does this for any bitrate and retention window, including quality settings other than BlackBox's.

Calls and microphone interruptions

Mobile operating systems allocate active microphone capture to one app at a time. That is a privacy feature — it is the reason two apps cannot silently listen at once — and it is the direct cause of most interrupted recordings.

If you take a handful of calls a day, continuous recording still works; you just get several files instead of one. If you are on calls constantly, continuous background recording is not the right tool: the microphone changes hands too often. A scheduled window over your quieter hours produces a more useful record.

The same logic applies to voice features. Dictation, assistants and text-to-speech are each short, but many short interruptions across a day fragment a recording badly. If you rely on voice typing all day, plan for a schedule rather than continuous capture. See another app is using the microphone for how to find and release whatever is holding it.

Continuous versus scheduled recording

Neither is better; they answer different questions.

Continuous suits you when you want a complete record of the day, have storage headroom, and do not take many calls. It is the simplest thing to operate — one tap in the morning — and it never misses something because it happened outside a window.

Scheduled suits you when you only care about certain hours, are tight on storage or battery, or take enough calls that continuous capture would be fragmented anyway. It costs less of everything, and there is less to check.

Scheduling uses a different mechanism from continuous recording, so continuous capture working perfectly tells you nothing about whether a schedule will fire. A schedule needs the app to still be alive at the start time and to be permitted to act: notification permission, exact-alarm permission on Android, no force-stop since the last launch, and a device clock in the time zone you think it is in. Test a window five minutes ahead before you rely on a real one — scheduled recording did not start covers the failure modes.

How to test recording reliability

Change one thing at a time and prove it. This ladder takes an evening and beats a week of guessing:

1. Restart the phone.
2. Start a 15-minute recording, lock the screen and put the phone down.
3. Check the file covers the full 15 minutes.
4. Repeat for one hour.
5. Repeat overnight.
6. Now introduce one interruption at a time — a call, then a voice assistant, then battery-saving mode, then switching apps — and note exactly what survives.
7. Write down the event that causes each failure.

Keep a simple pass/fail note for: 15 minutes locked, one hour locked, overnight, a call mid-session, app switching, and a scheduled start. The first test that fails names your cause, and the troubleshooter will tell you what to do about it.

Re-run the short version of this test after every OS update. Background behaviour genuinely changes between versions, and your own result on your own phone is worth more than any app's marketing copy — including ours.