Phone tapping is the act of a third party illegally intercepting the content of a phone call. In Japan, the secrecy of communications is protected under Article 4 of the Telecommunications Business Act, and violating the secrecy of communications is punishable by up to 2 years' imprisonment or a fine of up to 1 million yen (up to 3 years' imprisonment or a fine of up to 2 million yen for telecommunications workers) under Article 179 of the Telecommunications Business Act. Article 21, Paragraph 2 of the Constitution also guarantees the secrecy of communications, and infringing that secrecy is subject to criminal penalties.
Tapping methods differ significantly depending on whether the target is a landline or mobile phone. For landlines, physical connection to the phone line (tapping) is the classic method. Bugs are placed wherever the electrical signal of the call passes: the phone unit itself, modular jacks, or outdoor wiring boxes. Mobile phone calls, by contrast, are encrypted over the radio link, so intercepting the radio signal alone does not reveal the content of the call, and the methods used on landlines do not carry over.
However, mobile phone tapping risk is not zero. IMSI catchers (fake base stations, also called Stingrays) impersonate legitimate base stations to connect devices and intercept communications during relay. They are devices known to be used by law enforcement for investigations, but the very mechanism of impersonating a base station leaves room for misuse for criminal purposes. Additionally, if spyware is installed on a smartphone, not only call content but also SMS, location data, and camera footage can be monitored.
If tapping is suspected, take a step-by-step approach. For landlines, hire a specialist to sweep for bugs. Sweep fees vary by vendor and by the size of the building, so compare quotes from more than one firm. For smartphones, check for unfamiliar apps and update the OS to the latest version. For VoIP calls, using an end-to-end encrypted service such as Signal lowers the risk of interception along the communication path. In serious cases, consult the police and consider applying the Anti-Stalking Act or Unauthorized Computer Access Act. See Call Recording Legal Guide for the boundary between legal recording and illegal wiretapping.