Nothing overly exciting to play around with. But then again I work on them every day. Of course there is the fancier panels, like the HAI Omni panel I am working on today (burg, Lighting control, temperature control, music distribution.... all from a touch screen)
To answer your keypad question. Nope, not interchangable. Some brand have the ability to change keypads between lines, but other than that you have to have the same keypad with the same panel.
Be careful when you are buying off Ebay, alarm panels have this trickly little feature called "Installer lockout" The less reputable of alarm companies enable this feature ensuring nobody can default the panel back to factory. Simply put, this means your playing around would be very limited.
http://www.keepsafesystems.ca - KeepSafe Systems installs services and provides alarm monitoring services for security alarm systems in the Vancouver area of the Lower Mainland Fraser Valley British Columbia.
The KeepSafe Systems service area includes but is not limited to North Vancouver, West Vancouver, Richmond, Delta, Tsawassen, Ladner, Surrey, Cloverdale, Abbotsford, Mission, Aldergrove, Maple Ridge, Haney, Port Coquitlam, Coquitlam, Port Moody, Burnaby, New Westminster, Kamloops, Kelowna, Courtney, Comox, Nanaimo, Lions Bay, Squamish and pretty much everywhere in between.