An assay reader system incorporating a conventional assay reader, for example a lateral flow reader, and an insert aligned with the reader's sensor to detect an assay result. The insert may include a housing which defines a cavity to receive a removable barrier, wherein the removable barrier can be aligned between the sensor and the test strip. The barrier may include an optical window, and may be cleanable and/or disposable to maintain the accuracy of the reader. Test strips are introduced into the reader through a receiving port within the insert's housing. An air inlet on the insert further maintains the reader's accuracy by allowing air to be tunneled over the housing to remove excess dust, debris, or the like.