What does the Crystal "Lockdown" power do?

I finally managed to obtain my first Crystal crew member (finally!). I note that he has a "Lockdown" power, as shown in the screenshot below:

What does this power do? None of the tooltips I've seen provide any explanation. When is this power useful?

2 Answers

Lockdown: Active ability that coats the room they're in with crystals, preventing anyone from entering or leaving and making the room itself invincible to damage. The crystals wear off over time, or when attacked. This ability requires time to recharge after being used.

Source

9

The Crystal's Lockdown ability will block off a room with blue crystals, preventing damage & restricting movement by both friendly and enemy units.

From the FTL wiki:

Lockdown: Active ability that coats the room they're in with crystals, preventing anyone from entering or leaving and making the room itself invincible to damage. The crystals wear off over time, or when attacked. This ability requires time to recharge after being used.