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.
Before going into detail, here are the four routes available for tracing an anonymous caller, side by side.
| Route | Can it identify the caller? | What it requires | How heavy the process is | Limits to keep in mind |
|---|---|---|---|---|
| Block anonymous calls | No. It only stops the calls | Just subscribing to the service | Light. NTT's Number Request is a paid option, and mobile carriers offer equivalents | Calls from hospitals or certain public institutions may be blocked too |
| Keep a record of incoming calls | No, but it becomes evidence when you consult someone | Logging the date, time, frequency and the fact that the caller stayed silent | Light. You can start today | Records alone never reveal the caller. They are the foundation for the routes below |
| Consult the police. Call 110 in an emergency, otherwise #9110 | With a warrant issued by a judge they can obtain the caller's number from the carrier | Suspicion of a crime such as intimidation, stalking or obstruction of business by fraudulent means | Moderate. You wait for the police to decide whether to investigate | Simply finding the calls unpleasant is not enough to open an investigation |
| Bar association inquiry through a lawyer (Article 23-2 of the Attorney Act) | The inquiry can be filed, but disclosure is not guaranteed | You must have retained a lawyer for the matter | Heavy. It presupposes retaining a lawyer, and the fees vary with the case and the firm | The carrier may decline to answer, citing the secrecy of communications (Article 4 of the Telecommunications Business Act). Records are also erased after a certain period |
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 (a paid option) 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 warrant from a judge, 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. If the calls are silent, see also what lies behind silent calls and how to handle them.
Bar Association Inquiries Through a Lawyer
When the police do not act, the civil-side route that remains is a bar association inquiry: you retain a lawyer for the matter, and that lawyer asks their bar association to make an inquiry to the telecom carrier. Article 23-2 of the Attorney Act allows a lawyer, in a case they have been retained for, to ask their bar association to inquire with a public office or a public or private organization and request a report on the necessary matters. If the bar association considers the request inappropriate, it may refuse it.
Note that this differs from the "caller information disclosure request" used for internet postings. The regime for asking a court to order disclosure of sender information covers transmissions intended to be received by unspecified persons, such as posts on forums or social media, and one-to-one telephone calls fall outside that framework.
With that in mind, the constraints are as follows:
- A lawyer must be retained: This is not a procedure an individual files directly; it goes through a lawyer who has taken on the case
- Cost: Retaining a lawyer costs money, and the amount varies with the case and the firm
- No guaranteed answer: The secrecy of communications may not be violated (Article 4 of the Telecommunications Business Act), and a carrier may decline to respond to the inquiry
- Record retention: Carrier records are erased after a certain period, so traces thin out as time passes
Weighing the cost against the likely result, pursuing this procedure solely to learn who is behind an anonymous call is often impractical. Blocking anonymous calls first, and consulting a lawyer or the police only if the problem persists, is a more workable order.
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.
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 Persist
Anonymous nuisance calls persist for two reasons: placing calls has become cheap, and the mechanisms that hide where a call originates remain available.
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 place large volumes of calls automatically, with no human effort. 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, so enforcement rarely reaches them.
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" 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.