The past few seasons, Lions fans had to track ticket sales in the week leading up to a home game to make sure it sold out and the game was televised locally. Last year this wasn't a big problem considering seven of the eight home games were sellouts, but it wasn't often that a home game sold out more than a few days (or a couple days when an extension was needed) in advance.
This year, it doesn't seem likely that selling out games will be a problem. The first two games of the season were sellouts, and now you can add Sunday's game against the 49ers to the list. The Lions announced today that the Week 6 matchup is sold out, although some tickets that the 49ers returned are still available.
With the way the Lions have been playing, the demand is way up for tickets to their home games, as evidenced by this chart: