Disaster Message Dial (171) is a safety confirmation service provided by NTT during major disasters. Using a disaster-area phone number as the key, voice messages of up to 30 seconds can be recorded and played back. Activated when earthquakes of lower-6 intensity or greater or large-scale wind/flood damage occurs, it is easy to remember through the Japanese wordplay "i-na-i" (171, meaning "not home").
Usage is simple. After dialing 171, press 1 to record or 2 to play back, then enter the disaster-area phone number (home landline or mobile number). Up to 20 messages can be stored per phone number, with a 48-hour retention period. It can be used from landlines, mobile phones, and public phones, all free of charge. The web version "Disaster Message Board (web171)" also allows text message registration and checking, which may be more convenient from smartphones.
The Disaster Message Dial exists because of the call congestion problem during disasters. When major disasters occur, safety confirmation calls surge simultaneously, sometimes reaching 50-60 times normal call volume. Carriers impose call restrictions (up to 90%) to prevent network overload, making regular calls difficult to connect. The Disaster Message Dial has dedicated line resources reserved, enabling use even during call restrictions.
Advance preparation is important. Trial use is available on the 1st and 15th of each month, during Disaster Prevention Week (August 30 - September 5), and Disaster Prevention and Volunteer Week (January 15-21), so practicing actual operation with family is recommended. Particularly important is deciding in advance "whose phone number to use as the key." If all family members use the same number (such as the home landline) as the key, safety confirmation is completed simply by recording and playing messages for that number. Along with emergency numbers, review usage in the emergency phone number guide.