Paging systems have existed for an extremely very long time. You might not have recognized it however you are almost certainly presently using 1 in your everyday life! For example, some supporter controllers use easy primary radio frequency to switch on/from the admirers. Car critical fobs function the same way.  https://audio26000.tusblogos.com/29910518/5-simple-statements-about-eyeglass-places-near-me-explained