No, accessing hotel rooms with a smart phone is not safe. There are too many ways this could cause a problem. Cell phones are stolen all the time, and it would also be a target for hackers who want to use a cell phone to enter a room. Cell phones are not a safe tool to use for a hotel room key.
While I am all for technology and convenience, I would be a little worried about being able to access my hotel room via my smart phone. With all of the hackers out there it is only a matter of time before they are able to hack the system and access rooms. You go out and come back and your room is empty or worse, someone is waiting on you.
Why? I dont think thats a good idea AT ALL. There are very smart hackers out there, cell phones are NOT that hard to hack! It would be SO easy for someone to figure out how to hack into that and have complete access to your room. Or they could steal your phone... Terrible idea
It may not be safe to install hotel app as most of the app required access to your phone data,contacts, shared files, camera, microphone, online banking etc. also you will have to take your phone every where you go, like if you have to goto pool you will have to take your phone with yourself.