Gembok

Gembok (Indonesian for padlock) protects the apps you don’t want anyone else to open — messaging, banking, gallery — behind an overlay that re-arms the device biometric gate when a protected app is launched.

What it does

• Scans installed apps and lets you pick what to lock with a single tap.
• Uses the system BiometricPrompt rather than a custom lock screen — no stored credentials beyond the Android keystore.
• Detects when a protected app comes to the foreground and intercepts it instantly.
• Barely any memory footprint by design: the overlay is a lightweight Service + composition of the launcher activity.

Security properties

• No PIN/password stored by the app itself; authentication is delegated to the hardware-backed keystore.
• Protected apps are hidden from the recent-apps carousel while locked.
• Offer support on rooted devices kept minimal — the threat model is casual access, not a compromised device.

It started as a personal itch (a hand-me-down phone with curious siblings) and became a good exercise in Android lifecycle, UsageStatsManager, and keeping a Service polite to the system’s battery police.