Vanadium dioxide (VO₂) is attractive for a variety of applications in optics and electronics, due to its abrupt insulator-metal transition (IMT) with >10³× change in resistance near room temperature. Use of VO₂ in devices will require low power switching, with knowledge of the transition mechanism and behaviour down to nanoscale dimensions. To address this challenge, we use metallic carbon nanotubes (CNTs) with diameter ~1 nm [1] to probe nanoscale IMT in VO₂ for the first time. We find that a single CNT locally switches the VO₂ at less than half the voltage and power otherwise required. Furthermore, to understand the nanoscale IMT we use scanning probe microscopy (SPM) techniques to study devices during operation.