The most useful sensors?

I understand that this is quite a broad question, but would you mind listing the most useful sensors for your HA use case and the reasons for their usefulness?

Thanks.

Lux sensor for lighting control.

Bed sensor for switching everything off or starting my morning routine.

Lots of template sensors for predicting things like an estimate of my next electricity bill.

Camera object detection sensors for security alerts.

Mailbox sensor so I don’t have to walk down the drive unless there is actually mail.

Temperature and humidity sensors for climate and condensation control.

Hard wired PIRs for automatic lighting and security.

Zigbee contact sensors for house perimeter security and turning off heating/cooling if a door or window is left open.

Continuing on from Tom’s comment, I use a number of multisensors which have motion, temp, humidity and lux all in one. They are 5v powered so super fast and reliable which is great for smart lighting automation plus get used for my alarm. My lights turn on when there is motion and whenever the light level in a room is too low irrelevant of time of day. A single automation handles both on and off with all parameters accounted for.

@tom_l what hardware have you used for the mailbox? I bought some parts to do this a couple of years ago but haven’t installed yet.

I started out with ESPs but have move on to Aqara contact sensors for less battery hassles.

Ah ok, so just triggering on the letterbox flap? My letterbox doesn’t have an ‘in’ flap so I had planned on using a limit switch with long spring to sense things getting pushed in.

Triggering on the flap for mail delivered and triggering on the access door for clearing.

Water leak sensor, no use in 8 years and save me both time this year due to water issue in the kitchen.

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That is asking people why you like to go to the local carnival.

Some like the carousels.
Some like the beer vendors.
Some like cotton candy.

There are a 1000s answers.
But IMHO, the best answer is you can have all of them with Home Assistant.

The question was - what is the most useful sensor for you - it is clear that use cases and preferences are different.

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ESP32 BLE sensor that opens the front door as we arrive home.

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OK, I vote for taste and smell then. Oh and touch.

Integrations:
Insteon
Vizio
Xantech Media
Alexa
Chromecast
iBBQ

Sensors:
binary
Input_number
input_boolean
input_select
template
camera
rest
rest_command

They did not ask for a list of integrations or senors.

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For me, “useful” means “justifiable” in terms of time, effort and expense. The fun stuff is done mostly for convenience.

My first justifiable use case was temperature monitoring. If my pipes burst due to freezing temperatures, there would be a lot of damage, possibly making my house uninhabitable. Once that was in place, smart thermostats could be adjusted to save energy. Power-monitoring smart plugs allowed me to ensure my sump pumps didn’t get stuck on or off. Again, a failed pump could flood my basement, submerging the boiler and making the house uninhabitable.

Once HA was performing those basic safety functions, it became easy to add the “fun” stuff like controlling lighting and outdoor water faucets. And to start playing with automations, probably the most justifiable of which is creating realistic “away” lighting patterns.

There’s a nice custom integration in HACS that does this for you based on your own lighting use history.

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