Try Electromannsa.co.za
I have bought a couple of diy units from them and they work great. You need to load airtime or data (airtime doesn't expire, so works for me) on to the sim in the unit, then after the first year, there is a yearly subscription (R200) for the monitoring software. Obviously these systems work off cell reception, so can they can only monitor when in range of a tower. You can monitor from cell or PC, set up Geo fences for alarms, the system has decent history and there are even options to enable a mic and speaker, or cut or trigger an electronic device connected to it.
