?? LED will light itself in night to let other people found us in the first time. ?? ultrasound sensors on the backpack , able to detect the distance of about 3 meters , beeping sounds when you can know whether there is a suspicious person behind ?? If we are really in distress , the switch can directly open the backpack on the siren , to scare criminals associated with increased attention to the people around ?? through portable mobile power supply to provide a backpack when using a backpack can charge for their products is very convenient 3C ?? Turn on the alarm switch while the GPS location sent to the address of the phone and then send the police or a designated phone ?? backpack and cell phone to make a link , when the backpack 10 meters away from its own , the phone will sound an alarm to notify the backpack is to prevent theft