(from) under your nose idiom (US also (out from) under your nose)
C2 在…眼皮子底下发生（指坏事就在眼前发生但却没被意识到或无法被阻止）
used about something bad that happens in an obvious way but in a way that you do not notice or cannot prevent
She stole the shoes from under the assistant's nose. 她在售货员的眼皮子底下把鞋偷走了。