DENVER—After receiving the device intended to alert him when his family's table at the Cheesecake Factory was ready, local father Timothy Reardon traversed the parking lots of adjacent businesses with the pager Tuesday to determine its range. "I'll bet I can get all the way behind the Barnes & Noble, no problem," said Reardon, who has performed similar experiments with cordless telephones. "I don't want to take it too close to the Best Buy, though, because all that electronic stuff in there might screw it up." At press time, Reardon's wife and children were finishing their appetizers while Reardon was still trying to find a way to get off the roof of an Old Navy a quarter of a mile away.