应答器是利用电磁感应理论在特定地点实现机车与地面间相互通信的数据传输装置，安装于两根钢轨中心枕木上。

当列车上的查询器通过地面应答器时，应答器被查询器瞬态功率激活进入工作状态，并向查询器连续发送存储于应答器中的行车数据。

A balise /bəˈliːz/ is an electronic beacon or transponder placed between the rails of a railway as part of an automatic train protection (ATP) system. The French word "balise" is used to distinguish these beacons from other kinds of beacons.

Balises are used in the KVB signalling system installed on main lines of the French railway network, other than the high-speed Lignes à Grande Vitesse.