def active_zone(hass, latitude, longitude, radius=0):
    """Find the active zone for given latitude, longitude."""
    # Sort entity IDs so that we are deterministic if equal distance to 2 zones
    zones = (hass.states.get(entity_id) for entity_id
             in sorted(hass.states.entity_ids(DOMAIN)))

    min_dist = None
    closest = None

    for zone in zones:
        if zone.attributes.get(ATTR_PASSIVE):
            continue

        zone_dist = distance(
            latitude, longitude,
            zone.attributes[ATTR_LATITUDE], zone.attributes[ATTR_LONGITUDE])

        within_zone = zone_dist - radius < zone.attributes[ATTR_RADIUS]
        closer_zone = closest is None or zone_dist < min_dist
        smaller_zone = (zone_dist == min_dist and
                        zone.attributes[ATTR_RADIUS] <
                        closest.attributes[ATTR_RADIUS])

        if within_zone and (closer_zone or smaller_zone):
            min_dist = zone_dist
            closest = zone

    return closest