I actually made a combo traditional/digital dogtag by sandwiching an SD card between two tags in plastic liner. I chose a micro SD in its adaptor so that it can be read by a card reader.pda or I can just put the micro SD in my phone.
Its not really for first responders, but more a way for me to carry more detailed info such as serial numbers, scans of douments, photos, maps etc.
For fiorst responders, I have my name, National Insurance No. & NHS medical card No.