Yep, ADT doesn’t really make alarms - they just install DSC’s and change the installer code to something else to make your life a living hell (LOL) but you can find the typical codes they use on the net so it’s not the end of the world…haha. Swapping one DSC board with another is also a pretty easy job so if the board is slightly older, you can upgrade it without too much hassle if you’re not afraid of re-programming the new board. It’s maybe an hour or two of work at most.
it’s not 100% guaranteed that you have a DSC though, i imagine what you get with ADT depends largely on the area and what they’re currently offering…
If you have a DSC or honeywell panel, there’s already existing integrations into smartthings, you just need to buy an EVL-3 or EVL-4, assuming you have the right panel type…The best part about that is the envisalink device DOES come with full call center alarm monitoring service, if you pay extra for it, and it’s quite cheap. Like under $10 cheap, and fully accredited, you’ll get your insurance discounts for it.
For ST integrations, my alarm integration covers DSC only, but there’s honeywell ones out there as well. The nice thing about this route is you can have both, which it sounds like is exactly what you want. I have yet to try their alarm service either, but I likely will once I’ve stabilized my system a bit more (i’m always testing it out as part of my development, I don’t wanna send the police here just yet, lol)
Also, I bet this is your cheapest option by far. The EVL device is like $70-90, and if your alarm is compatible, that’s all you need. If your alarm isn’t compatible, an entire DSC PC1864 v4.6 kit, which comes with alarm keypad, alarm system board, metal enclosure, battery, transformer, and wireless remote, and siren, is like, $120 or less, I’ve seen it as cheap as $50-80 for the board alone, and that’s often all you’d need to replace all the existing stuff you have with an up-to-date system that can be used with EVL-4 and ST. You can re-use all the hard-wired sensors as-is. Only wireless sensors are an issue, if the old system wasn’t DSC, but most old systems don’t have wireless sensors at all…Needless to say, you could have an entire DSC system with ST integration for less than say $200-250, and the monthly fee would be like $8/month for monitoring. But you will have to do some of the work yourself, if you’re up for it.