The Desire to Know Who Is Calling
Repeated anonymous calls in the middle of the night, eerie silent calls that hang up immediately - wanting to know who is behind them is a natural reaction. However, the reality is that identifying an anonymous caller is extremely difficult for an ordinary individual.
When a caller dials with the anonymous setting (prefixing the number with 184), the recipient's phone does not display the caller's number. This is a legitimate feature provided by telecom carriers for privacy protection. Yet it is also frequently abused. Dealing with stalker phone harassment and anonymous nuisance calls is a problem many people face.
What You Can Do on Your Own
Block Anonymous Calls
The simplest and most effective measure is to block anonymous calls entirely. NTT's "Number Request" service (220 yen/month) plays an automated message to anonymous callers asking them to redial with their number displayed, and the phone never rings. Mobile carriers also offer anonymous call rejection services.
However, blocking is "prevention," not "identification." It does not tell you who the caller is. If you need to identify the caller, a different approach is required.
Keep a Record of Incoming Calls
Recording the date, time, frequency, and content (silent or spoken) of anonymous calls is important evidence if you later consult the police. As explained in the evidence collection guide, organize call history screenshots, call recordings, and notes in chronological order.
When You Consult the Police
Can the Police Identify Anonymous Callers?
The answer is yes - the police have the technical means to identify anonymous callers. The anonymous setting only hides the number from the recipient's phone; the caller's number is still recorded in the telecom carrier's systems. If the police obtain a search warrant, they can request the carrier to disclose the caller's information.
However, the police need "suspicion of a crime" to act. Simply being annoyed by anonymous calls is not enough to trigger an investigation. The following situations are more likely to prompt police action:
- Threatening content: Statements like "I'll kill you" or "I'll set your house on fire" (criminal intimidation)
- Extreme persistence: Dozens of calls per day, repeated calls in the middle of the night - conduct exceeding socially acceptable bounds
- Part of stalking behavior: Combined with following, lying in wait, or other stalking conduct (Anti-Stalking Act)
- Business disruption: Repeated silent calls to a company or store that interfere with operations (obstruction of business by fraudulent means)
How to Consult the Police
Start by calling the police consultation hotline (#9110) and explaining your situation. For urgent cases (e.g., you received a threat), call 110. Bring your call records, any recordings, and a chronological summary of the incidents to make the consultation more productive. See also the police consultation guide.
Caller Information Disclosure Requests Through a Lawyer
Even if the police do not act, a civil remedy exists: a "caller information disclosure request" (hasshinsha jouhou kaiji seikyuu). This is a legal procedure asking a telecom carrier to disclose the caller's information (name, address, phone number).
However, this procedure has several hurdles:
- Attorney fees: Typically 200,000 - 500,000 yen
- Court approval: The court must find that "the infringement of rights is clear"
- Time: The process often takes several months to half a year
- Record retention period: Carriers generally retain communication records for three to six months; records may be deleted if too much time passes
Given the cost-benefit ratio, pursuing a disclosure request solely to identify an anonymous caller is often impractical. A more rational approach is to block anonymous calls first and consider legal action only if the problem persists.
What Is Technically Impossible
The internet is full of ads for "apps that display anonymous caller numbers" or "services that identify anonymous callers," but these are scams or misleading advertising. The anonymous setting conceals the number at the telecom network level, and no phone app can override it. Home security cameras for physical evidence collection are a far more realistic countermeasure.
The term "reverse tracing" appears in dramas and movies, but real-world tracing is performed by the police with carrier cooperation - it is not a service available to individuals. Focus on stopping the calls themselves by using nuisance call blocking methods.
Why Anonymous Calls Are Increasing
Anonymous call volumes have been trending upward in recent years, driven by changes in telecommunications technology and increasingly sophisticated criminal tactics.
The Spread of IP Telephony and Anonymity
The proliferation of IP telephony (VoIP) has dramatically reduced the cost of making calls. Using overseas VoIP services, it is possible to place large volumes of calls to Japanese numbers at very low cost while concealing the caller's identity. Fraud groups based overseas can route calls without going through Japanese carriers, making identification even harder.
Prepaid SIMs and virtual phone number services in some countries allow phone numbers to be obtained without identity verification. When such numbers are used to call Japan with the anonymous setting, even carrier logs may not reflect the true origin, and police investigations take longer.
Advances in Number Spoofing Technology
Caller ID spoofing technology has also advanced. Some criminals deliberately display real numbers (such as police stations or city halls) to deceive recipients, but many still choose the anonymous setting to avoid the risk of spoofing being detected. For criminals, anonymous calling is the lowest-risk method because it leaves no trace on the recipient's end.
Abuse of Auto-Dialing Systems
Robocall systems can automatically place thousands of calls per day. Combined with the anonymous setting, criminals can mass-dial anonymously and deploy scam scripts only on answered calls. See also how to spot robocalls. These auto-dialers are often operated from overseas servers, outside the jurisdiction of Japanese law enforcement, making regulation an ongoing challenge.
The Best Defense Against Anonymous Calls
Since it is technically impossible for individuals to identify anonymous callers, the most realistic defense is simply not answering anonymous calls. Enabling NTT's Number Request (220 yen/month) or your mobile carrier's anonymous call rejection service will automatically block anonymous incoming calls. Check landline nuisance call settings for specific setup instructions and start protecting yourself today. Making a habit of not answering anonymous calls alone dramatically reduces the risk of falling victim to fraud.
Note that blocking anonymous calls may also block calls from hospitals or certain public institutions. If this is a concern, use voicemail as a supplement - if a message is left, you can call back. The goal is not total blocking but finding the right balance between minimizing risk and not missing important calls.