Detection of Tungsten Hexafluoride
$\ce{WF6}$ is not an uncommon gas used in industrial manufacturing of semi-conductors. Commercial gas detectors are readily available, and will detect $\ce{WF6}$ down to low ppm range, which is about an order of magnitude less than the $\mathrm{LC}_{50}$ for rats, apparently.

You could google tungsten hexafluoride detector, but some examples include (no affiliation or endorsement):


http://www.newcosmos-europe.com/gas-by-name/144-tungsten-hexafluoride-detection.html 
http://www.toxicgasdetection.co.uk/gas/?gas=Tungsten%20hexafluoride&amp;search=Tungsten%20hexafluoride&amp;form=gas&amp;id=416 
https://www.gas-find.com/hexafluorure-de-tungstene.html 


The most common type of detector is a diffusion monitor with electrochemical sensor.
Some sensors actually use conversion of $\ce{WF6}$ to $\ce{HF}$, and then detect the $\ce{HF}$. Commercial $\ce{HF}$ detectors at low ppm range are also common.