The invention creates a method for identification of a physical unit (M) in an open, wireless telecommunications network by means of a testing device (P), having the following steps: storing a secret identity (SIMEI) and an open identity (IMEI) in memory in the physical unit (M); generating a first parameter (CHv) in the testing device (P); sending an identity request (IR) with the first parameter (CHv) from the testing device (P) to the physical unit (M); generating an electronic signature (SIGt) by means of a first cryptographic function (F3) from the secret identity (SIMEI) and at least the first parameter (CHv) in the physical unit (M), and sending the generated electronic signature (SIGt) and the open identity (IMEI) to the testing device (P); generating the secret identity (SIMEI) from an open key (EMIGK) and from the sent open identity (IMEI) in the testing device (P); generating a corresponding electronic signature (SIGv) by means of the first cryptographic function (F3) from the generated first secret identity (SIMEI) in the testing device (P); and identifying the physical unit (M) by a comparison of the electronic signature (SIGt) sent and the corresponding electronic signature (SIGv) in the generated testing device (P).