GoKawiilBefore diving into kill switches, let's establish a baseline for how a VPN functions. VPNs hide your IP address by creating an encrypted connection between your device and the VPN server before you connect to a website. By linking these three destinations (your device, VPN server and destination) with encrypted tunnels, VPNs make it harder for outsiders to spy on your internet traffic or conduct man-in-the-middle attacks. Meanwhile, a VPN also helps hide your browsing activity from advertisers, websites and your internet service provider.
A kill switch helps protect your privacy in case this connection drops or falters. While enabled, the kill switch monitors the quality of your connection to a VPN server. If it detects an irregularity, the kill switch will block your device's internet connection. This prevents your IP address or DNS queries from being exposed, since that's the reason you're using a VPN and even a short exposure can be compromising.
Many VPN kill switches will also do this whenever you switch servers, providing an extra layer of protection that mitigates the potential for DNS leakages during automatic reconnection. Once the tunnel between your device and server is back online, your VPN will reestablish your device's internet connection.
Modern VPN kill switches operate either on an application or system level. For app-specific kill switches, your VPN will only block connections for selected apps that may leak sensitive data to outside observers. System switches, on the other hand, cut off all internet traffic to your device to prevent lapses in identity protection.
Application switches provide flexibility, letting you protect your browser traffic while updates and video-calling apps continue on. System-level switches (also known as network kill switches) are more effective, but may result in frequent disconnections if you have a spotty connection.