One easier way to detect (without jamming afterwards), for iOS at least, is to install the "Fing" app, connect to the wifi and scan the network. Then you will know the connected devices and their names. Chances are that cameras will have easy to recognize names on them. EDIT: you'll get the MAC address too, so you can compare if they match camera companies.
Edit: Having now installed Fing and looked at what it does, it seems to basically just look at its assigned IP and netmask to determine the address space of the local network, and then perform an nmap-style ping scan to see what doesn't time out. When it gets a packet back, it uses the MAC address to identify the type of device, and a PTR lookup with the DHCP-provided DNS server to obtain a hostname. These are pretty cool capabilities to have on a handheld device, of course, but if you can't or won't install Fing, you can do pretty much everything it does with a 15-line Perl script on any device that can connect to the wireless network.