A simple inexpensive sensor that detects hydrogen peroxide vapour that can be used to sniff out peroxide-based explosives, such as those used in the July 2005 bombing of the London transport system, has been developed (F I Bohrer, C N Colesniuc, J Park, I K Schuller, A C Kummel, W C Trogler; J Am Chem Soc, 2008, 130, 3712)