In theory, there are indeed some technical means that may be used to intercept VoIP calls, especially when the call is not encrypted or the encryption implementation is flawed. These technologies may include： 1. Man-in-the-middle attack: An attacker may try to insert himself between the two parties to the communication, intercept and possibly modify the communication data. 2. Network sniffing: On unsecured networks, unencrypted VoIP packets may be captured. 3. Malware targeting the terminal: audio may be captured at the device level. However, modern VoIP services usually use strong encryption (such as TLS/SRTP) and other security measures to prevent such attacks. Services that use end-to-end encryption (such as Signal, WhatsApp, etc.) further improve security. To protect yourself, it is recommended： -Use well-known VoIP services with a good security record -Ensure that devices and apps are kept up to date - Use a secure Internet connection -Consider using additional encryption tools Interception that is completely "undetected" is very difficult because modern systems usually have multiple layers of security protection and monitoring mechanisms.