There are many actually!
Foremost, if they live alone in the house (at least spend the most part of the day alone), video intercom is a security essential. Whoever comes at the door, before allowing them inside, they can see and talk to them.
(Courtesy: Product Review)
If the house is big and has more than one entrance or open space, a smart alarm is another important security-centric technology for seniors. If someone tries to enter the house unauthorized, the alarm will go off, alarming the seniors, as well as everyone around. This can give them peace of mind all the time.
A smart smoke alarm is also something very important. Detecting any smoke, it would set off, alarming everyone about the fire to act quickly.
Installing devices in the home like Amazon Echo or Google Home is also highly recommended. Since seniors forget quickly, such smart AI can remind them things… like when it's time to have medicine, when they should eat and exercise, and so forth.
Smart lighting is also a good option. It would eliminate them the inconvenience of remembering to switch off the lights all the time. Once they leave the room, the lights would go off automatically.
If they are your parents and you're really concerned about their well-being, you should definitely install a home security camera. The live (and recorded) feed can be cast directly in your Smartphone no matter where you are. So, you can always be sure that your parents are safe and fine.
In addition, although this isn’t a smart "home" technology for seniors, having them wear Smartwatch or fitness band is important. It will help track their health, capturing all their vitals and informing them (and you) about their fitness and health overall.
(Courtesy: Wearable Devices)
I am sure, there exist many other smart home technology for seniors. But the above-mentioned are the ones that I think are essential.
Hope this answers your question. :)