Some DIY systems are self-monitored, which means you'll receive alerts when devices are triggered, but it's up to you to contact the local authorities if there's a break-in or a fire. However, DIY vendors are increasingly offering professional monitoring services; some require a contract and some allow you to pay as you go so you're only being monitored when you need it, such as when you're away on vacation.
I have experienced ADT security at several different places I have lived. The customer service reps are very professional and helpful. We experienced one bad experience where the alarm was going off for some technical reason but we received the phone call and the alarm sent the police to our house. It was a big mess but the only time that ever happened and considering the rest of the time our customer service was exceptional so we kind of over looked the one bad experience.
I had ADT come in and have their system put in my home I had just purchased. It took 3 hours to install. They had a promotion going on with a free ring camera. But keep in mind. The home when I bought it had a security system already hard-wired into the home. Which was working. I just needed to have a security company come in and take over the system. The salesman told me they would piggy back my system. They did exactly what they said. 45 minutes after the installation was done. I tried to arm the system. It came up with multiple error codes. I called ADT and the salesman who set this up. He said the tech who installed it will call me back in 30 mins. This was a Saturday. Well no call.
ADT offers 24/7 professional monitoring of your home security system 365 days a year. Beyond its most basic equipment package and monitoring plan that look like the rigorous security systems of the latter part of the 20th century, ADT now also offers home automation through its app, ADT Pulse. This includes a control panel with Z-Wave compatibility, giving you the flexibility to add whatever smart home devices you’ve already got in play, from lights and locks to appliances.