Yes, you can join Indian Army through B.Tech in ECE through Combined Defence Services commonly known as CDS is conducted twice a year by Union Public Service Commission (UPSC) for graduate candidates who wish to pursue their career as commissioned officers in Army, Navy and Air Force.

Also, you can go through the direct recruitment (Graduate Technical Entries) as there are 4 channels for the same like UES, TGC, SSC(Technical) and AEC.

To know more about the same,you can go through the below link -

Direct Recruitment

Good Luck!!!