So just got my new entry door installed and with it, my new Schlage Connect lock. Am using the RBoy stuff with it as well.
Question is, while we normally don’t leave the front door open, am wondering why I should add a sensor. What logic have you all used when deciding if/when to integrate a sensor like this? What sensor did you use and why?
The main reason people add an open/close sensor on the front door is so they don’t try to lock the door when it’s open because then when someone tries to close the door the bolt will smash against the door frame. Whether that’s useful to you or not is up to you. We don’t need it in our house.
The main reason people use an open/close sensor on an interior door to the garage, a door to the backyard, or side yard is because then they will know if that door has been left open, usually by kids. If you have to go around the house and check the doors from time to time, then this is useful. 
The main reason people add a vibration sensor is because they want to try to create an alert when someone knocks on the door. But those tend not to be reliable: you get a lot of false alerts unless you add yet another sensor, such as a pressure mat under the welcome mat. Otherwise just the wind shaking the door can set it off. Or kids running past it on the inside of the house.
Did that help?
As far as which sensor, there are many different factors that go into this choice, including cost, whether you want zigbee or zwave or something else, personal aesthetics, etc. Also whether you wanna temperature sensor built-in.
The Device class features FAQ covers many of the different types:
Bulbs, switches and sensors, oh my....what to buy (device class features FAQ)
If you have the money, it’s hard to beat the Sensative strips. Zwave, available In both the US and the UK. These have a patent on a very Slim long lasting battery, so you can put them in the door frame and paint them and they will be nearly invisible. 10 year battery life. Works well with smartthings in either app. But expensive, usually around $60 each. Sometimes on sale for around $50.
Aeotec Makes a recessed sensor where you drill a long hole in the door frame. So this one is also invisible, but more work.
After that there are lots of different brands at lots of different prices. Smaller ones are usually more expensive.
I use contact sensors on all of my doors that have locks, well really all my doors, interior and exterior, have contact sensors…because it gives you a time stamp as to when the door(s) opened and closed.
For example,
If front door stays closed for 30 minutes
And
Front door lock is unlocked
Then lock
Or
If back door is open
Then do not lock
Or
If back door stays open for 3 minutes
And
HVAC is cooling
Then turn off HVAC
Or
If motion changes to active
And
Front door closed in the last 2 minutes
Then lock
Or
If motion changes to active
And
Door is closed
Then set room to occupied
Pause all automations
Contacts are super useful for me and that’s why I use them on all doors!
