Comment by blantonl

Pagers don't have SIMs, they are simply programmed with a "Cap Code" which is basically the address of the pager.

Pagers can be programmed with multiple cap codes, and can function differently based on which cap code address receives a message. For instance, a single cap code could be programmed to just vibrate the pager, vs an audible alert.

Pagers are sent out via very high power distributed transmitters as one way transmissions simulcasted transmissions.

The format is typically:

[CAP CODE] - Message

That's literally it.