Simplex 4098-5214 Duct Housing No RelayThe Simplex 4098 5214 duct smoke sensor housing enables a 4098 5252 MX Technology smoke sensor to monitor for smoke conditions in air conditioning or ventilating ducts. A sampling tube, selected in accordance with duct width, is installed into the duct, allowing air to be directed to the smoke sensor mounted in the housing and is discharged back into the duct by using the exhaust tube.