The picture is of a pager. A pager (also known as a beeper) is a wireless telecommunications device that receives and displays alphanumeric messages and/or receives and announces voice messages. One-way pagers can only receive messages, while response pagers and two-way pagers can also acknowledge, reply to, and originate messages using an internal transmitter.

Pagers were developed in the 1950s and 1960s, and became widely used by the 1980s. In the 21st century, the widespread availability of cellphones and smartphones has greatly diminished the pager industry. Nevertheless, pagers continue to be used by some emergency services and public safety personnel, because modern pager systems' coverage overlap, combined with use of satellite communications, can make paging systems more reliable than terrestrial based cellular networks in some cases, including during natural and man-made disaster. This resilience has led public safety agencies to adopt pagers over cellular and other commercial services for critical messaging.

More Info: en.wikipedia.org