If you're not in the area or are simply unable to watch the Lions' preseason games live, you will be able to catch them on NFL Network. All 65 of the NFL's preseason games will be shown on NFL Network in HD at some point, and one of the Lions' games will actually be shown live. The other three will be replayed the day after the game, which still isn't bad.
Here is the full schedule of when the Lions' preseason games will be on NFL Network:
Sunday, Aug. 22 - 1 p.m. - Detroit Lions @ Denver Broncos
Saturday, Aug. 28 - 5 p.m. - Cleveland Browns @ Detroit Lions (LIVE, although it will probably be blacked out locally)
Friday, Sept. 3 - 12 p.m. - Buffalo Bills @ Detroit Lions
All times are Eastern.