Continuing on my thoughts, I forget which project it is for since here are a few, the R-Pi2 and Banana Pi are for more serious computing as for their CPU Power and RAM (and the SATA Drive on the B-Pi). The R-Pi Models A/A+ and B/B+ are for smaller smart devices like intelligent robots (Arduino are for drones - user controlled robots), and better for prototypes and actual units.
One project I'm doing is a Cigar Box Laptop, but stupid Muslim Stores don't want to give up their cigar boxes they sell out from even when I offered to buy them. They just rip'em up... damn bastages. When I was a kid, you went to a corner store and asked for an empty cigar box, they give you 2 or 3! As is, I got it battery powered on one of those external cellphone batteries for about 4 to 6 hours on just the R-Pi board (rated for 2600MAh).
http://www.ebay.com/itm/Portable-Power-Bank-External-3000mAh-Mobile-USB-Battery-
Charger-for-Cell-Phone-/351114026059?pt=LH_DefaultDomain_0&var=&hash=item51c006dc4b It's the screen that eats up all the power.
As I see it an Arduino should be used as for the keypad as it would be running around in locked up mode instead of the R-Pi, which would hold the access information. It the input matches an entry on the database, the R-Pi would send a signal to open the lock to that unit. Any tempering or if the Arduino goes dead, the lock is set to the lock on that unit. The problem is to set up an ID Program so that more than one Arduino can talk to R-Pi. As is, there is no ID and it can only one Arduino can can talk to the Raspberry Pi. Or in the case of the Mega Arduino - which has over 50 I/O Channels, have one Ardunino handle all the locks but you still need an Arduino for the key pad for each door. Its the keypad that's mucking everything up.