Anyone with a cell phone and a free app can see any network broadcasting, whether or not they have the SSID or password. If someone is in range, given the right tools and time, they can get in. MAC spoofing is simple. Getting the SSID is simple. Passwords can be tougher, if complicated and long enough. For most of us, with a reasonable password, the expense and time to crack it far exceeds the return on whatever we have to get stolen.
My biggest concern is making sure I can get reception in our hot tub .
Personally, I buy my own modem, and a separate router. I do not like the rental or provided ones, since they often do not allow you to access all of the settings (to try to keep you from asking for help).