While they cannot see the actual person entering the password, they do enforce device count restrictions. My guess is that's it's more than 4 brings trouble.

My wife occasionally uses my monthly pass and I've been locked out of my account on two different occasions. I typically log on with 3 different devices (iPhone, iPad, Macbook) and if my wife logs on with more than 1 new device, the account gets locked out for having used too many devices.

A simple inflight chat with customer service always gets a free day pass, but they cannot override the lock so you must wait until the device count resets monthly.