What Is a VPN Kill Switch?
A VPN kill switch is a security feature that blocks all internet traffic the moment your VPN connection drops. Without a kill switch, if your VPN disconnects unexpectedly, your device reverts to your regular internet connection and your real IP address is exposed. A kill switch prevents this by cutting your internet access until the VPN reconnects.
Why the Kill Switch Matters
VPN connections drop due to network congestion, device sleep/wake cycles, ISP throttling of VPN protocols, or server-side issues at the VPN provider. Without a kill switch, each drop briefly exposes your real IP.
Torrenting: Your real IP gets shared with every peer in the swarm the moment the VPN drops. ISPs, copyright monitoring firms, and law enforcement log these.
Sensitive communications: Even a brief reconnection without the VPN exposes your real IP to the destination server.
Public Wi-Fi: A VPN drop on an untrusted network exposes your traffic to whoever is monitoring it.
How a Kill Switch Works
Most VPN clients implement the kill switch as firewall rules at the OS level. When the kill switch is active, the firewall allows traffic only through the VPN tunnel interface and blocks the regular network interface. When the VPN drops, no traffic flows until the tunnel reconnects.
System-Level vs. Application-Level Kill Switch
System-level: Blocks all traffic when the VPN drops. Most secure.
Application-level: Blocks only specific apps (e.g. your torrent client) when the VPN drops, while allowing other traffic to continue. More flexible but less secure.
Best Kill Switches in 2026
Mullvad: Lockdown Mode blocks all traffic outside the VPN tunnel even when the Mullvad app is not running. The most comprehensive implementation available.
NordVPN: System-wide kill switch that has been independently tested and works reliably including during fast reconnects and sleep/wake cycles.
ProtonVPN: Reliable system-level kill switch with option to block even when VPN is off (pre-connection protection).
ExpressVPN: Network Lock works on Windows, Mac, Linux, and routers. Reliable in independent testing.
Avoid: Many budget VPNs advertise a kill switch but only close the app process when the VPN drops. Traffic continues to flow. This is not a real kill switch.
How to Test Your Kill Switch
- Connect to your VPN. Note your VPN IP via ipleak.net.
- Force-disconnect the VPN (close the app or toggle Wi-Fi off/on).
- While the VPN is disconnected, try to load any website.
- If the kill switch works, the page will fail to load.
- If the page loads and shows a different IP, your kill switch is not working.
Kill Switch vs. Always-On VPN
A kill switch reacts to a disconnection and blocks traffic when it happens. Always-on VPN prevents disconnection from being possible at the network level. Always-on VPN is more secure. For daily use, a system-level kill switch provides adequate protection.