There would be several ways for the cameras to get a live signal to Nolan's computer.
One would be satellite (i.e. what television news has been doing for decades), but as the cameras are indoors, that's not a real possibility.
A second would be for the whale cams to connect to the local WiFi router wherever they're placed, and with Nolan's hacking skills this is a theoretical possibility, but it would require a lot of preparation - he'd have to hack each individual WiFi network and then encrypt all his intrusions so that the whale cams couldn't be tracked.
The third possibility, and by far the most likely, would be for the cameras to transfer their stream via cellular technology... any smartphone can already do this. You would just need the camera, a 4G radio, and a battery, and it could then transmit to a server that Nolan could log into and watch the live streams. Something like these, for example.
More support for this last possibility has to do with NolCorp - though it hasn't been explicitly stated, it has been very subtly implied that NolCorp manufactures mobile technology... in episode 2 of season 1, the big announcement about which company would be making components for a NolCorp product is reminiscent of Apple always making such a big deal over who makes their components. What's more, the ABC site has a series of supposed memos that Nolan wrote to his company, and one of them mentions how the NolPad will be better and faster than the iPad or Samsung tablets. If NolCorp makes mobile technology, then a 4G hidden camera makes more than enough sense for the fiction of the show.