The Collaborative International Dictionary of English v.0.48:

pager \pag"er\, n.
   A small electronic communication device which signals when a
   telephone call has been received at a base station. Each such
   device receives radio signals from the base station
   specifically coded for the individual to whom it is
   registered; the signal given by the device to the registered
   user may be a beeping sound, indicating that the user should
   call the base station to receive a message; or it may display
   a telephone number to which the user may call directly to
   return the incoming call, or may display a short message.
   Such devices are small enough to carry in the pocket or
   pocketbook, or to clip onto a belt or other part of the
   clothing. Also called beeper.
   [PJC]

WordNet (r) 3.0 (2006):

beeper
    n 1: an electronic device that generates a series of beeps when
         the person carrying it is being paged [syn: beeper,
         pager]

The Free On-line Dictionary of Computing (30 December 2018):

pager
beeper
bleeper

   1.  (Or "beeper", "bleeper" (UK?))
   A small wireless receiver that, when triggered (generally via
   phone), will beep or vibrate (un)pleasantly.  The wearer will
   have been trained to respond to this signal by looking at a
   small screen on the device for an unimportant message.

   In recent years, pagers have grown more complex, allowing for
   long alphanumeric messages to be received and scrolled
   though (as opposed to earlier models, which supported only
   short numeric messages); at the same time as pager functions
   are integrated into some PDAs.  If this trend continues, the
   distinction between PDAs and high-end pagers will
   disappear.

   Short Message Service allows a mobile phone to display a
   message, just like an alphanumeric pager.

   2.  A program for viewing a text file a screenful at a
   time via a text terminal, as opposed to scrolling through it
   in a GUI window, or catting it all at once to the
   terminal.

   The best known pagers are more, less, pg and list.com.

   (1997-09-11)