The proliferation of GNSS-receiving mobile devices in the consumer market and the growth of the Intelligent Transportation Systems sector have raised a lot of interest in low-cost precise positioning. However, GNSS signal quality is degraded inside the metal body of a vehicle, which is where the antenna of a portable device is to be located. This article investigates the effect of antenna location on precise low-cost GNSS positioning for a road vehicle. We compare a roof-mounted GNSS receiver with an identical receiver having the antenna on the dashboard and a tailored smartphone also located inside the cabin; both the availability of raw carrier phase measurements and the resulting horizontal precise point positioning accuracy are evaluated. The test results show that the 90 % circular error probable is degraded by several meters inside the vehicle. Moreover, most of the evaluated accuracy metrics indicate that the low-cost GNSS receiver with antenna inside the cabin achieved a positioning accuracy at least 50 % better than the smartphone located next to it when using the same satellite systems.