Rather than going hi-tech, with some expensive add on, or rigging something up off your sprinklers designer Casey Schneider has come up with a simple solution to watering your plants while you are away - Water from a Stone.
Here is a quick description from the Vendor's website:
Keep your plants perfectly watered! Water From A Stone slowly lets water out into your planter over the course of 3-4 days. A useful addition to any gardener's home. Made from hand-blown glass. Holds 7oz (207ml) of water.