This just popped in my twitter, and it looks like something interesting for the kindof forgotten HW section.
It is based on an Arduino, a GSM modem and a small NRF board for the wireless sniffing. All that packed in a standard USB charger case. All the code is available in gihub.
Even when it is a bit old, I think it is a great example of HW hacking. Take a look to the code to figure out how some stuff work... how to send data via an old GSM modem, sniff RF signals,...