Smatree Key Ring Wireless Bluetooth Cell Phone Lost Reminder, Mobile Chain, Remote Control Key Ring with Timely Alert , Cell Phone Protector 1pcs It works on cellphones with the function of Bluetooth. Remind .U reminds you do not forget your cell phone. Supports standard USB 5V charging. Build-in rechargeable Li-ion battery. We will send one of the three colors randomly. While your first time use, please charge the battery power for at least 2 hours.