Are they monitoring sales of gas masks? ...ear plugs?.....latex gloves?.......safety glasses? That sort of thing? Were the propane tanks full or empties? The Boston bombers used a cellphone to trigger their pressure-cooker, if I am not mistaken.
The mass cellphone reports were from individuals - no monitoring or that of any other commodity. Doubt if the jihadis would have any use for the items you mentioned. Safety is last on their list.
Tanks were full - is report on FR somewhere today or yesterday I think.
If barrel bombs, look for compressed air equipment to go missing.
Whatever you do; do NOT place a mixture of acetylene and oxygen in a trash bag and...