There are many forms of security. There is security to detect if someone is entering your home or leaving your home. There is security to detect fire or CO in your home and alert you or if you’re not home, notify an alarm monitory service.
There are a lot of options for addressing each of these possible scenarios. If you have a trust worthy local company, I urge you to contact them. Especially when it comes to life safety for Fire and CO detection there is no substitute for a good professional security company. This does not mean I endorse large, heavily advertised companies or the first result in a web search. I just want you to at least try to find someone who can help you create a reliable and properly installed Life Safety system. When dealing with this sort of equipment it is NOT the company as much as it is the individual who knocks on your door.
If you find that you need to do it yourself, then I will try to provide as much useful information as I can.