Half a century after their debut, Japan’s pager services will finally cease on Tuesday, bringing an end to what was once considered a must-have communications tool by high school girls before the advent of mobile phones.

Tokyo Telemessage Inc., the nation’s sole remaining pager provider, said it would begin shutting down the radio signals behind its services at around midnight Monday.

In recent years, the tiny device had been favored mainly by those working in hospitals, where cell phone use was once discouraged because of concerns about poor reception and the disruptive effect that electromagnetic waves can have on medical devices.

Dubbed pokeberu (pocket bells), sales of the devices in Japan began in 1968 with the predecessor of NTT Corp. To reach someone, callers would dial a pager number from a landline, causing the device to beep to notify the owner.

Initially, pager services were used by companies to communicate with sales staff who were out of the office. But from the late 1980s onward, their popularity grew because they could be used to display short messages by creatively combining numbers and text characters.

In the 1990s, female high school students drove the pager boom further as they came up with clever combinations to exchange messages.

Among the short numerical messages were “33414,” which in Japanese can be pronounced “samishiiyo,” meaning “I’m lonely.” Another was “999,” a series of three (san) nines (kyū) that was a casual way to say “sankyū” (“thank you”).

Pager users exceeded 10 million in 1996. However, from around that time, beeper services began to decline with the arrival of mobile phones. Subscribers decreased further as email, texting and taking and sending photos by phone became standard.

Though NTT’s mobile unit, NTT Docomo Inc., terminated nationwide pager service in 2007, Tokyo Telemessage continued to operate in Tokyo and neighboring Saitama, Chiba and Kanagawa prefectures.