A creepy stalker
Being constantly aware of your surroundings can save your life. Even though we’d like to give strangers the benefit of the doubt, there could be one odd folk out of the pack that means to do harm to any random person on the street.
While the OP was walking home, they spotted a passerby in an all-red outfit. The guy looked drunk or like he was on drugs, so the OP sprinted straight for their coded gate. After gaining entrance and locking the gate behind them, they found the guy in red standing there. He was staring at them for 10 seconds before running back the way he came from.