Why Your LINE Calls Drop When You Lock Your Screen, and How to Fix It

You press the side button on your phone to turn off the display, slip the handset into your pocket, and the conversation suddenly dies. For millions of daily voice callers on LINE, this abrupt disconnect is an infuriatingly common reflex failure. What is supposed to be a simple command to turn off a battery-draining screen ends up hanging up on friends, clients, or family members.

The issue stems from a clash between system-level power button behaviors and the way messaging platforms interface with your mobile operating system. While traditional cellular calls have evolved to handle screen sleep smoothly, VoIP apps like LINE rely on a patchwork of platform settings, background permissions, and accessibility toggles. Fixing it takes less than two minutes once you know where the conflicting controls are buried.

📌 Quick Summary:

• The Direct Culprit: Both iOS and Android feature legacy call-handling rules where the physical power button acts as an instant hang-up command.
• The Platform Split: Apple isolates the fix inside Accessibility menu toggles, while Android distributes power-button termination across manufacturer-specific accessibility and dialer configurations.
• VoIP Audio Integration: LINE's "Integrated Calling" feature determines whether your phone treats a LINE call like an official cellular call or a fragile background app task.

The Mechanical Conflict Between Display Sleep and Call Termination

Smartphones carry a hardware paradox: the physical side button serves as both a screen-sleep switch and an emergency end-call trigger. In early smartphone design, pressing the lock key to hang up was seen as a convenience feature, giving users tactile confirmation that a call was terminated without needing to look at touch targets.

Modern communication platforms broke this logic. Users routinely stay on voice calls for hours using wireless earbuds, speakerphones, or wired headsets. In these situations, keeping an OLED display burning at 1,000 nits in a pocket makes no sense. Users tap the side key expecting display sleep during call operations, but the operating system intercepts the click as a call-drop command.

On LINE, this conflict is worsened by the transition between foreground app states and background services. If the operating system interprets the side-button click as a hardware interrupt rather than an ambient display dimming request, it tears down the audio pipeline. What should be a seamless transition into side button sleep mode becomes an unintended lock screen call disconnection.

How to Stop the Side Button from Ending LINE Calls on iPhone

Apple introduced a direct toggle to stop this behavior in iOS 16, yet millions of users still struggle because the switch is hidden outside the standard phone and app settings.

To prevent the side button from dropping your active LINE voice calls on an iPhone:

Open Settings, navigate to Accessibility, and select Touch. Scroll down until you see the toggle labeled Prevent Lock to End Call. Turn this switch ON.

When enabled, pressing the physical side button turns off the screen immediately while leaving your voice connection untouched. You can put the phone in your pocket or face down on a desk without severing the link.

There is a second critical requirement within LINE itself: CallKit integration. LINE relies on Apple's system framework to handle calls identically to regular carrier connections.

Inside the LINE app, tap the Settings (gear icon) on the Home tab, navigate to Calls, and verify that Integrated calling is switched on. If this toggle is off, LINE runs as an isolated third-party audio process, making iOS background call handling far more prone to aggressive system memory purges the second the screen goes dark.

Disabling the Power-Button Hangup Across Android Devices

Android handles hardware-button triggers differently depending on whether your handset runs stock software, Samsung's One UI, or proprietary skins from Xiaomi or Motorola. The power button ends call setting is typically active by default on many commercial builds.

Device Ecosystem	Target Setting Location	Required Configuration
Apple iOS (iOS 16, iOS 18)	Settings > Accessibility > Touch	Toggle "Prevent Lock to End Call" to ON
Samsung Galaxy (One UI)	Settings > Accessibility > Interaction & Dexterity	Open "Answering and ending calls"; toggle off "Press Side key to end calls"
Google Pixel (Stock Android)	Settings > Accessibility > System controls	Turn off "Power button ends call"
Xiaomi / Redmi (HyperOS / MIUI)	Settings > Additional Settings > Accessibility > Physical	Disable "Power button ends call"

On stock Android installations, including Google Pixel devices, head to Settings, tap Accessibility, select System controls, and find Power button ends call. Switch this off.

Samsung Galaxy owners must navigate through an extra sub-menu. Go to Settings, choose Accessibility, and tap Interaction and dexterity. From there, select Answering and ending calls and toggle off Press Side key to end calls.

Once disabled, pressing the power button simply cuts off the panel backlight. Your microphone and speaker channels remain open. To end the call, you must unlock the screen and press the red disconnect icon inside the app, or use the disconnect button on an external audio accessory.

Addressing Background Memory Killing and Proximity Sensor Glitches

Adjusting button settings resolves roughly 85% of unexpected disconnections. The remaining drops usually point to aggressive memory management or sensor hardware failures.

When you lock your phone, aggressive battery optimization profiles monitor background memory. If your device runs low on system RAM, the operating system looks for background tasks to suspend. While native phone calls receive kernel-level priority, third-party VoIP apps are vulnerable unless explicitly protected by LINE app permissions.

On Android, grant LINE unrestricted battery usage. Long-press the LINE application icon, open App info, navigate to Battery, and change the setting from "Optimized" to Unrestricted. Ensure that Background data usage remains enabled under Mobile Data settings. If your phone restricts data the instant the screen locks, the audio stream drops within three seconds, mimicking a hardware hangup.

Proximity sensor malfunction presents a related, deceptive problem. Smartphones use an infrared or virtual proximity sensor near the top earpiece to detect when the phone touches your ear, automatically shutting off the screen to prevent stray cheek inputs.

If a dirty screen protector, pocket lint, or a damaged sensor blocks this mechanism, the screen stays illuminated during calls. Users feeling the screen against their face instinctively press the side button to force the display off, inadvertently hanging up the call. Regularly clean the front speaker grille and verify sensor functionality using diagnostic dial codes or support apps to rule out physical hardware issues.

Systemic App Permissions That Destabilize Background Audio

Microphone management and peripheral routing also destabilize calls during power-state transitions. Bluetooth audio connections can complicate this behavior.

When you tap the power button while connected to wireless earbuds or a car system, the device attempts an audio handover. If the connection fails or drops bandwidth, LINE's default failsafe protocol may sever the call entirely rather than fall back to the phone's internal earpiece.

To ensure stability across all modes:

Review the specific permissions assigned to LINE. On both iOS and Android, confirm that LINE maintains uninterrupted access to "Microphone," "Nearby Devices" (critical for Bluetooth latency), and "Background App Refresh." Disabling any of these background entitlements creates a timing mismatch: the moment the hardware power button signals a display freeze, the operating system revokes audio stream privileges, terminating the connection.

Regularly updating LINE through the App Store or Google Play Store also prevents regression bugs. Messaging protocols evolve alongside major operating system updates; older app versions often struggle with power state transitions on newer OS builds.

Frequently Asked Questions (FAQ)

Q1: Why does my LINE call hang up even after I turn off "Power button ends call"?
A1: If the hardware toggle is disabled but the call still ends when the screen turns off, the issue is likely battery optimization or data restriction rather than the button itself. Set LINE's battery usage to "Unrestricted" in your device settings and verify that Background App Refresh is enabled. If your phone enters deep sleep and cuts background data, the call drops instantly.

Q2: Will enabling "Prevent Lock to End Call" on iPhone affect regular carrier phone calls?
A2: Yes. This is a system-wide setting within iPhone accessibility touch settings. Once enabled, pressing the side button will never terminate a regular cellular call, a FaceTime call, or a LINE call. You must always use the on-screen red hang-up button or controls on your headphones to disconnect.

Q3: Does turning the display off during a LINE call save substantial battery?
A3: Yes. Modern OLED displays consume significant power, particularly at medium to high brightness levels. Turning the screen off while continuing an audio-only conversation can reduce battery consumption by 40% to 60% over an hour-long voice call, while also preventing device overheating.

Keeping Your Conversations Connected

Accidental call drops on LINE are not random app glitches. They are the direct result of legacy operating system controls overriding contemporary communication habits.

By adjusting the side-button settings on iOS or disabling call termination toggles across Android, you decouple your screen's power state from your active calls. Take a moment to adjust these controls, grant LINE unrestricted background permissions, and you can pocket your phone mid-sentence with complete confidence that your call will remain online.