The Lockdown Puck is a sensor that allows you to monitor your gun safe in a number of ways. The Puck delivers information on temperature, humidity, and access to your smartphone or tablet and it works everywhere you have Wifi.
The Lockdown® Puck™ is a state-of-the-art monitoring and security device that provides true peace-of-mind with real-time notifications and control using the Lockdown Logic™ App. Track temperature and humidity, movement, and when something is opened anywhere in the world. Whether you’re securing your vault, front door, or vehicle, with a touch of a button, Lockdown what matters most.
Utilizing state-of-the-art sensors and our proprietary algorithm to detect tampering, the Puck™ will notify you instantly anywhere in the world. The built-in Wi-Fi and Lockdown Logic App connects directly with your smart home and other Lockdown Devices. From protecting guns and ammo to your family heirlooms, you can trust the Lockdown Puck to keep your valuables safe and secure.
You can learn more at Lockdown.com
I use this https://www.ihomeaudio.com/iSS50/ which is both HomeKit compatible and half the price. Plus, I paid $30 on an Amazon sale. Working great for years!