Apple AirTag​​ 

Here is the link to add an airtag in the "find my" app https://support.apple.com/guide/iphone/add-an-airtag-iphf666e9559/ios -Jazzy

AirTags can be found using the Find My app on your iPhone, tap the Items tab and select the AirTag to locate it on a map, play a sound or enable lost mode. ~Brian

AirTags can be detected up to approximately 30-100 feet (9-30 meters) using Bluetooth directly from your iPhone or other Apple devices. However, they can be tracked much further thanks to Apple's Find My Network, which leverages the Bluetooth signals of other Apple devices within a 30-100 foot range to relay location information to you. This allows for tracking potentially anywhere in the world where there are other Apple devices connected to the internet ~Balter

Battery life is around one year with regular use. https://support.apple.com/en-us/102600 -Melissa

AirTags are compatible with any iPhone, iPad, or iPod Touch device capable of running iOS/iPadOS 14.5 or later. -Red

Yes, Apple indicates it requires iPhone SE, iPhone 6s or later with iOS 14.5 or later. For more information please visit https://support.apple.com/contact -Katie

An AirTag uses Bluetooth to track its location, with a typical range of around 30 to 100 feet. -Danielle

The Apple Air Tag has a replaceable battery. -Toni

No. They use a battery which can be replaced when needed. Apple includes details on replacing it on their website here: https://support.apple.com/en-us/102600 -Josh

Yes, you can check their location via the Find My app. ~Freddy