Just discovered this thread about home automation so let's go and excuse my poor english !
My installation is more than 15 years old at a time Zwave Zigbee and all those "automation boxes" didn't exist, started slowly to learn and find usage to keep grand'ma at home as long as possible (no way for me to send her to those horrible nursing home).
I did it first as cheap as possible on my own (not much money), mostly 1-Wire and X10 technology and installed 12 x DS18B20 1-Wire Temperature sensors in the house including in the fridge, the gaz boiler and the freezer down to the cave, thru a **very** long 2 x wire.
I record and graph them every minute and that produced about 12 x 1 500 000 records that is usefull when I do have some database test/bench to do ;-)
This graph helped to understand many things happening in the house (now a country house as grand'ma passed), especially how it react when boiler is turned on each Friday, how the house get hot, how long it takes for heat cycles become stable.
And answer is "12 hours", first circle is very long, long enought to reach the max water Temp of the boiler and stay there, second circle show the walls are now warmer and it takes lesser time to reach target temp, third circle show a stabilized cycle 12 hours later, with a 2 hours cycle including 30 mins of heat (yes this house need some energy saving enhancement) :
And also when the cave has been flooded and freezer sank, it's amazing the amount of information you can guess from temperature curves !
First square on the left, no more power in the house because of the water reached the motor of the freezer, shortcut pushed main power down, the bottom line is the freezer, the one up is the fridge, then I got an alert (my little server and DSL router are on UPS), second square power is back (called a neighbour, country house, I am not here), third water continue to flood the cave and freezer started to float and toopled and water is a very good heat conductor, next square I am at home, open the freezer to check in and close it fast, last square i get all the stuuf and move it to my neighbour's freezer, as you can see, those T° curves are an open book when you know how to read them
Other example is when the guy from the boiler's maintenance came for its yearly visit made a mistake in boiler heat settings, this appeared immediately on the curves, power has been set to 50% instead of 80%, was in winter, had to call him back to fix the problem.
X10 still in place to check all doors/windows opening including freezer and fridge that trigger an alarm in case they are open too long.
Installed also many IR sensors to check last room activity and detect if grand'ma stand too long in a room where she should not (2H in bathroom in not normal for example, did she fell ?) or check if she wake up on time and moved around in the morning (she's still in bedroom at 10 a.m ? let's give her a call to check if she's ok and just want to stay a bit more time in bed but not because she feel bad).
Once I got an alarm because she was not at bed at 11 p.m (not normal and old people have their own same day-by-day timing), I checked living room camera and saw she fell on the floor, so I took the car and here I go.
I also installed an infrared emitter to control the TV (useless today but usefull to setup the prefered channel and tv show at the right time coz grand'ma was too mind lost to use TV remote control anymore).
Added also a flush counter to check if she go there "enough" (many old people died because of "intestinal blockage") then call a nurse if something go wrong.
Then I added an Asus EEE-PC with skype running full screen automatically when incoming video call from familly (and IR transmitter turned TV off at same time) so grand'ma could talk easy without touching the netbook with no disturbing TV sound.
Had also to make some limnous path at night so when she wake up and wanted to go to the bathroom during the night she did not need to find the light switches, small light turned on as she put foot on the floor and walked (all IR sensor based).
Of course many IP cams where there (not in bedroom nor bathroom), mainly Axis, not a lot of choice at the time and expensive 330€ each (but I do not regret as they are still running 10 yers later except one !), I had also to develop my own VMS/CMS-like system coz existing ones were expensive and did not have all the features I needed so I started my own from scratch.
Today I am playing with micro controllers (Arduino/ESP8266) and also Raspi so I make my own IoT modules for example with the very usefull tiny and cheap BME280 that is an all in one Temp/Humidity/Pressure I2C sensor and I send data to Thingspeak :
I will soon buy a dehumidifier that I want to fully follow/control remotly and know how long it run per day (so you much it cost), check the water level and get warned when tank is full and may be add a water level monitoring (many ways to do it but i'll try with a small VL53L0X distance lazer sensor, extremly precise up to 2m) to check how fast tank get filled and calculate some "full tank" ETA just for fun, may be I could also add some pump system with a long flexible pipe to empty the tank if it get filled to fast in the week when I am not here (rememeber... country house).
Home automation is more fun when you DIY