Low-cost (~US$20 to 30) Qualcomm-based LTE mobile hotspot (also branded Kajeet RC400L) that exposes a /dev/diag diagnostic interface, the reference, best-tested hardware for running EFF's Rayhunter IMSI-catcher detector. The TP-Link M7350 is also supported; in principle any device with a Qualcomm modem exposing /dev/diag may work.
Lifecycle not assessed: nobody has checked yet whether this tool is still maintained, sold or working. Check the project's own page before relying on it.