Keypad on arduino

So i recently got an Arduino mega, then I moved into a house with an old security system. I can't find the plug for the control panel, but I want to attach the control keypad to my Arduino that way I can use the original keypad to kinda rebuild the system.

Welcome to the forum.

So, what are your questions?

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If the keypad has a matrix of buttons with one connection per row and one connection per column, I would use the Keypad library.

it has 2 power lines and 2 data lines, so there are only 4 connections

That could be almost anything. Have you got a two-channel oscilloscope?

No, i don't have an oscilloscope or any fancy equipment. something that might help is that i'm using a mega 2560, and the alarm keypad is this. Ademco 6127 Keypad [Honeywell 6127] - $0.00 : AlarmSuperStore.com, Your One Stop Alarm Shop

That does help. The inside of one such alarm keypad shows that the two data lines for a remote keypad are IN and OUT. That means it's not a Wiegand interface that uses 0 and 1 lines for send-only data. My guess would be 'async serial' and all you would have to do is figure out the baud rate and message protocol.