Python tool that reads the GSMTAP stream produced by gr-gsm and pulls the IMSI / TMSI identities the network pages over the air, printing the cellphones it sees around you. A PASSIVE IMSI catcher, it harvests identities off the broadcast/control channels without transmitting anything (no rogue cell); the active catcher is a rogue BTS (osmo-bts / OpenBTS).
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.