Oh my, a question targeting my hardware experience AND my more than passing interest in cognitive science!
I have a friend who is currently dying from Muscular Dystrophy. In the end stage of this disease, he is barely able to move any part of his body. He and I investigated several consumer-grade EEG devices as a means of him controlling computers (none ended up working for him as well as voice command). In the course of that investigation, we initially rejected the NeuroSky MindWave Headset, but I am returning to it now as an ideal solution to your problem.
While it has a pretty crappy sensor configuration, it is my understanding that seizures are large events which any EEG machine should be able to detect relatively easily. The upside to this machine is that it is cheap and relatively unobtrusive compared to other available brands. Moreover, this device is able to interface with mobile devices via bluetooth and does have a developer's kit app for Android available for purchase. I'm not going to go into how you solve the software side of this problem, because this is a hardware recommendation only (as befits the site), but I trust since you are inquiring you'll know where to go from here.