MLB tells teams to have metal detectors in place by 2015
Increased security will soon be in place at all 30 MLB parks.
"This procedure, which results from MLB's continuing work with the Department of Homeland Security to standardize security practices across the game, will be in addition to bag checks," said MLB spokesman Michael Teevan.
As the AP notes, the Mariners will have such measures operational in time for the upcoming season.
As with all such security measures, the challenge is of course striking a balance between safety and customer convenience, and it will probably take some time to find that balance.