I have a question that maybe someone knows or can point me in the right direction: we I moved into our house 9 years ago, the previous owners had a home security system which they left behind… it included wireless (433mhz) PIR sensors throughout the house (most of them are still there because they were not in the way and I never bothered to take them down)… now that I am automating everything with HA I was wondering if these sensors typically use some standard protocol that I could use or if they are normally proprietary and not worth my time??? If they are proprietary then I will probably take them all down, scavenge for part and move on, otherwise if someone could point me in the right direction on how to interface with them, that would be great.
If you can receive the MHz codes then definitely use them 
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If you don’t mind a bit of soldering, there are two 433MHz gateways described in the forum.
The first link actually has a list of the protocols it decodes, and the second has a thread somewhere of the devices that people are using with it.
I use the second one with some success.