Installing a Simplisafe…how do I disconnect old ADT system?

I’ve just bought an old house that had an ancient DSC keypad and alarm system. Transformer is nowhere to be found but disconnected from the circuit and I’ve removed the leads from the back-up battery. I’ve read several posts that say I can just put the wires back in the wall but they are too long to fit back in the wall and when I put an electricity tester over them they still beep as if they’re hot. If I turn off power to the house, can I just cut the wires? Will they be a danger if they are live and back in the wall once I turn the power on? The electrician I called said they don’t work on alarms.

submitted by /u/ETTATX
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