A connecting lock for tire chains, comprising an elongate receiving opening for receiving two chain links, framed by a first longitudinal crosspiece, an opposed, a second longitudinal crosspiece interrupted by an insertion opening, and two transverse crosspieces. The compounds of formula are useful building blocks, in particular in the synthesis of electrically conducting polymers. The antenna includes contacts in the hybrid circuit to couple the metallic traces to electronic devices in the hybrid circuit. Each air intake path is provided with a separate air-filter. The indicator systems include an indicator device coupled to an explosion-proof enclosure.