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2.
Amazon Echo - I have 8 Echo devices in my home (2 of the "big" Echo cylinders and 6 of the small Dots). I have them spread throughout the house to ensure there is voice coverage everywhere and it is working pretty well. Actually, I haven't deployed the 8th unit yet - the Dot in my kitchen is on top of my refrigerator and is close to the Dot in the adjacent room, so I'm thinking about moving it to a more central location and then I'll take the 8th unit and install it in the garage or maybe my car.

3.
Logitech Harmony hubs - I have 3 of the Harmony Home hubs integrated with SmartThings and two of them are controllable with Echo (I need to get the third one added soon). I used them to control my home entertainment devices but they're very flexible and can control almost any IR device - I have a portable AC in my office since central air can't cool it fast enough with all my equipment, and I can use Harmony to power it on and off.
4.
Blink cameras - I have 10 Blink cameras spread throughout the house, focusing on entry points, my dog's cage, and my office. One is on my front porch, protected from the elements. I've preordered one of their external cameras and will probably eventually deploy a second, "exterior" Blink camera network with 3 or 4 exterior cameras.