Disregard my comment, I thought the feeder was dirty but it’s just a bunch of sunflower seeds

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Not sure if this is what you’re describing, but phones like the one you pictured have a reversible tab for use if you mount the phone to a wall - if the tab is sticking up, it keeps the receiver from falling off the cradle.

Here’s a site selling them, but it has a diagram showing where it’s located:

https://www.zcover.com/store/catalog/zCProduct.php?wp=WP_CI881CTR&zPath=212-213-255

I’ve run it on an iPhone 5 or 6, I don’t recall… had it watching my living room for a month while I was away, and aside from a few false positives when light patterns changed due to the wind blowing tree branches around, it was excellent.