@alowhum There will be a wealth of information out there on the net and probably also at your local library. look for resources about remote cabin power systems and also even the larger 5th wheeler type caravan systems will be helpful reading. You will also need to check your local building codes to see if there are any rules to be adhered to.
When we built our house (about 15 years ago, long before i discovered MySensors we ran a low voltage backbone cable throughout the house. From this backbone we ran smaller cable drops to every room in the house. Many of these are still not in use but as others have said the cost of running wires is relatively cheap when you are building. Of course we still have mains power as well and use the low voltage system to compliment this.
In those initial years the 12v system was used primarily for lighting systems such as night lights etc. As time progressed we installed 12v outlets in the bedrooms and these now are used to power bed/reading lamps. The small 12v downlights have also proved to be very easy to convert over as well. These were initially halogen bulbs but now there is a good range 12v LED replacements for just about any type of socket. Once I discovered MySensors and home automation then the 12v system became even more useful now powering several nodes and even the gateway.
Right from the start we ran our system from a battery with solar charging and in 15 years it has never let us down. Voltage drop will always be a thing to watch, but with LED's low power draw and as you have surmised the ability of arduinos to run well below 12v it will usually be of little practical concern. Unless of course you are thinking of running more than lights and nodes.
Can I assume that you are using power to DHT22 via a FET or directly from Arduino pin, so you are controlling when the DHT22 is getting power/voltage?
I personally think using a DHT22 that requires min 3.3 V is not a good option for battery device - but I understand it can be managed
My opinion is is use HTU21D instead since it can operate on a much lower battery voltage. Watch out, some breakout boards have a 3,3V voltage regulator, that is just using battery consumption and isn't needed when using Arduino 3.3V 1Mhz battery operated
@mirodin said in How to power my sensors in a rental?:
using normally closed reed switches
You can "convert" those by reverting the orientation of the magnet on your door, then adding another magnet (weaker or further away) inside the node enclosure to keep the reed switch closed when you open the door. When the door is closed the reversed magnet on the door will open the reed switch.
To do even better you can use :
reed switches with 3 leads that work as both normally opened and normally closed switches, and wire them to the 2 interrupt pins. I used that on my first nodes and managed to get reeeeaaaally long battery life on a simple CR2032. When door status changes the node is woken up then you set pin low and current could run only a very short time, you send the message with new status then you activate the other interrupt pin and go back to sleep https://www.aliexpress.com/item/33028519094.html
if you're not afraid with SMD there are some ultra low power hall switches, using less than 1uA of current like the DRV5032.