A device for use in the correct application and monitoring of the technique of ACF (Applied Cricoid Force) during tracheal intubation comprises a cylinder (1), a piston (2), seal (10) and either an aneroid gauge (3) or a calibrated spring (6) which provides resistance to force applied to the device and at the same time permits monitoring of the force applied. The device may also or alternatively be used as a training tool on a suitable patient substitute e.g. a table, bench or a manikin, until the trainee gains the experience and skills which enable them to reproduce the correct force when applying cricoid force directly on patients.