"Sensors detect you at 50% less range, allowing you to get closer before being marked."
Stealthy allows players to get closer to the base before the Radar Sensor makes their IFF show up. Base Turrets and deployable turrets will also take longer to target the player. This is a Primary Perk.
Upgrade 1: +20% sensor evasion range
Upgrade 2: +20% sensor evasion range
Upgrade 3: +30% time for turrets to target you (1.3 seconds for base turrets and .715 seconds for deployable turrets)
Infiltrators can benefit from this perk as it also affects the range of Jammers, which interfere with their stealth abilities.