I use the Simplisafe system in my RV. It has door and window, smoke, temperature sensors etc. Install it yourself in a few minutes. It uses cellular, has text alerts for power failure etc. The text alerts work great as you know instantly of power out etc. I have been using it for a couple of years with no issues. It is wireless so you change batteries every year or so. It also has remote keychain fobs. It has a keypad to use inside the coach.
The few times it has activated, my mistakes, they called rapidly. The only problem is they want to call police but since I never know where I will be located they cannot. Sometimes if we are going to be in one location for a few months I will call and change the address so they know where I am located. It also has a cell phone app you can check the inside temperature and activate and deactivate the system. We have dogs so the temperature checking along with power failure feature gives us peace of mind in the summer.
It does have a monitoring fee but it is low and worth it to know the dogs are ok.