When purchasing a pre-owned smartphone, physical defects like cracked glass are obvious, but damagedinternal antennas remain invisible to the consumer. Reception failures following handover are significant driversof resale disputes; however, current on-device “RF tests” conflate hardware quality with local environmentalattenuation. We present Cross-Band Antenna Health Inference (CBAHI), a 90-second on-device test thatdifferentiates hardware deficits from environmental factors on stock Android. CBAHI captures concurrentreception data across WiFi (2.4/5/6 GHz), Cellular (LTE, 5G NR), GNSS, and Bluetooth-LE. Our corecontribution is a leave-one-out studentised residual test with an exact t-distribution null, allowing for calibratedp-values. We evaluated CBAHI on 420 physical devices tested in the Retronics refurbishment laboratory. Thecorpus spans 120 healthy calibration units and 300 labelled test units across Samsung, Google, and XiaomiOEMs, incorporating documented water damage, post-screen-replacement, post-back-glass-replacement, anddrop-history cohorts. Zero false-positive hardware-concern flags were observed in the cross-environment stresstest (60 runs across environment shifts), while the full labelled-cohort evaluation at η = 0.01 yielded one falsepositive out of 120 healthy devices (specificity 99.2%). Each result is signed by a hardware-attestedAndroidKeyStore key bound to a buyer-supplied nonce plus the device’s IMEI hash, mitigating replay, twindevice substitution, pre-caching, and band-uniform selective-environment manipulation. The system achieves aweighted sensitivity of 87.1% for documented water and mechanical damage (C1–C3), supported by adifferentially-private federated protocol with cohort-rolling keys. We further characterise the system through aper-band Bayesian posterior baseline, a software-perturbation grid that exercises the graceful-degradationbehaviour of the leave-one-out test under partial radio loss, and a cross-environment validation yielding zerofalse-positive hardware-concern flags across a > 13 dB cellular shift, a > 7 dB-Hz GPS L1 shift, and anopposite-direction Bluetooth shift. We are explicit about what we do not claim: per-antenna isolation (closed atthe OEM combiner firmware), graded NFC sensitivity (binary functional check only), and reliability inpathological RF environments. A flagged band is a hint to inspect, not a verdict.