In certain aspects, the present disclosure provides a monitoring device that includes a condensation unit and a detector, such as a proportional detector. The condensation unit includes a condensation surface, a cooler abutting the condensation surface, and a collection vessel in fluid communication with the condensation surface. The monitoring device may include a decomposition reactor, such as an electrolytic reactor or a reactor that includes an active metal, such as an alloy of sodium and potassium. Particular implementations include a housing that at least partially encloses the condensation unit. The housing may include an aperture, which may be covered by a screen, mesh, or filter. The housing may also include a fan. The fan is used, in some examples, to draw air through the aperture. The monitoring device is, in some implementations, configured for remote operation, such as including a power supply or transmitter.