A Villari effect seatbelt tension sensor 10 comprises a sensor housing 50 having a plunger chamber 52 and a tongue head flange chamber 54 therein. The two chambers 52 and 54 are separated by a radial flange 58 extending therebetween defining a passage connecting the chambers. A Villari effect sensor 12 is disposed axially within the sensor housing 50 and is secured on one end 16 to a plunger 40 disposed within the plunger chamber 52 and secured on the opposite end 14 to a tongue head flange 20 disposed within the tongue head flange chamber 54. A tongue 24 connected by a shaft 28 to the tongue head flange 20 has a slot 26 therein for securing a seatbelt 80 thereto.