Under what circumstances can I connect to someone else's wf for free?

Someone else has turned on WiFi, 1, and there is no password. If your device is detected, it can connect. However, if the other party has any monitoring software and sees a strange connection device, the screen will be black, so it can only be connected once. 2, set a simple password, you can connect with software such as WiFi cracking. (only provide answers, and do not advocate surfing the Internet)