Representative apparatus, method, and system embodiments are disclosed for non-invasive detection an ingested battery or magnet in a human or other animal subject. The various apparatus embodiments include one or more Hall effect sensors, arranged in a hand-held embodiment or arranged along a flexible strip having an adhesive. A calibration may be determined or reference or calibration field measurements may be generated. A flexible strip is arranged, or the hand-held embodiment is moved, over the esophagus of the subject to generate target magnetic field measurements. The presence of an ingested battery or magnet is detected when one or more target magnetic field measurements (or gradient) is or are greater than or equal to a first predetermined threshold, or when a sign reversal occurs for a difference between target and reference measurements. The various apparatus and system embodiments may also include a monitor for signal processing and display of results.
