Receive up to $504 promo credit ($180 w/Welcome Unlimited, $360 w/ 5G Start, or $504 w/5G Do More, 5G Play More, 5G Get More or One Unlimited for iPhone plan (Welcome Unlimited and One Unlimited for iPhone plans can't be mixed w/other Unlimited plans; all lines on the account req'd on respective plans)) when you add a new smartphone line with your own 4G/5G smartphone on an eligible postpaid plan between 2/10/23 and 3/31/23. Promo credit applied over 36 months; promo credits end if eligibility requirements are no longer met.
Easiest way is simply change your SSID (network) password.
the harder way is to set a ip assignment to each device you want, then select the option that no one can join your network.
do the first suggestion it’s much easier.