Yes, there are alternatives to using Amazon Sidewalk for the sensor. You can use either a Ring Bridge or a Ring Alarm Pro Base Station to add the Ring Mailbox Sensor to your home network if you don't feel comfortable having your devices connected to Amazon's low-bandwidth wireless network.
The antenna enhances the Ring Mailbox Sensor's functionality by extending the device's range and avoiding interference issues that may be caused by a metal mailbox. It allows the sensor to communicate with the Ring Smart Bridge or other Amazon Sidewalk-enabled devices, ensuring reliable notifications when the mailbox is opened.
The Ring Mailbox Sensor costs $29.99 on Amazon. It is a smart device that sends alerts to your phone when your mailbox door is opened, helping you keep track of mail deliveries.