Messaging device opening up electronic records primarily (5)

I believe the answer is:
pager
'messaging device' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'opening up electronic records primarily' is the wordplay.
'opening' becomes 'gap' (gap is a kind of opening).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'primarily' suggests taking the first letters.
The first letters of 'electronic records' is 'er'.
'gap' in reverse letter order is 'pag'.
'pag'+'er'='PAGER'
Can you help me to learn more?
(Other definitions for pager that I've seen before include "Old electronic bleeping device" , "Bleeper device" , "message on this?" , "Small radio bleeper for contact" , "Electronic alerting device" .)
