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As some of you may know, I am going currently working on a theater project. For IR control, I plan to use an Ocelot, with buttons hooked up to an SECU-16. After looking around, I found out about keypads, and they use a matrix system. Basically, one button connects two sets of contacts. So I could program the Ocelot Logic to react based on the connections, and initiate an IR action.

I have found one like This one, but was wondering if anyone know of a place that also sold keypads, so I could have a bit more of a selection to compare.
With SECU16 inputs you will need individual contacts, not a matrix. A matrix requires the electronics to be specifically designed for them. A keypad matrix works by scanning, applying a voltage on a row and then looking for that voltage in one of the columns to indicate a keypress. It does this row by row many times per second.
Hmm, okay. I was looking at This diagram, and it looked like when you pressed a button, let's just say button 1, it would make a complete circuit using connectors one and 5.

Does the keypad need power, since it is scanning many time a second? Are there other keypads that do what I want them to do?
Most keypads you will see are raw matrixes, ie: just the contacts. The one in your link is a raw matrix. Like I mentioned, you need to design specific electronics and program code (or scanning hardware) in order to use a matrixed keypad. The SECU16 cannot use this type of arrangement.

How many different inputs do you need for your project? The SECU16 has 8 inputs, while the SECU16I has 16.
I was going to get the SECU-16i, becuase it has 16 inputs. A keypad with 16 buttons would be great, but I can work with something that has less.