Holo-sensors or bio-sensors were sensors that were essential in the mapping of Naboo's watery core and Ohma-D'un's surface. They were primarily utilized by ER-1 probe droids. The sensors mapped out any biological activity and sent back any positive finds to the probe droid. The readings were then analyzed by the probe droid and forwarded relevant information, sound through its comlink and live holofeed through its remote sensor platform, to a holoviewer or another holographic device. They functioned in a similar fashion to lifeform scanners.