The "metal can" is almost definitely a single port SAW resonator.
wikipedia briefly mentions resonators under this page if anyone is interested in the physics but it wont help you diagnose the unit:
The popular frequency around 433Mhz tends to be 433.92Mhz.
Modulation for data with these circuits tends to be OOK (on/off keying). i.e. either the rf circuit is transmitting a "carrier" on 433.92 or not.
Epcos has a good app note on saw resonators. Most relevant will be the schematic at the endhttp://www.epcos.com/web/generator/Web/Sections/ProductCatalog/SAWComponents/AutomotiveElectronics/OnePortResonators/PDF/PDF__AN1,property=Data__en.pdf;/PDF_AN1.pdf
I think resistor R12, a 33K (marked 333) is probably going to be your guy. check which side goes to the smd transistor(kind of hidden under a coil in your photo). My bet is that the other side of the R12 goes towards the "blob".
From what i've seen, the bus pirate can diagnose a number of protocols and interfaces. Don't be surprised if the manufacturer has gone for a proprietary protocol. Also, manchester encoding is a popular encoding method for this type of transmitter. Will bus pirate diagnose manchester? There are a few types of manchester encoding though.
There's a number of vendors that sell cheap (<$10) 433.92Mhz receiver modules if you wanted to use that as a diagnosis tool.
Also, I have a cheap 'n nasty radio frequency counter i got off ebay (~$30 - ~50)that i use to check if such an rf circuit is transmitting. You'll probably find that if you apply VCC through a 33k to the same place where the r12 connects to the transistor, you can probably get the transmitter to fire up a carrier on 433.92Mhz. That's if the RF circuit works at all. When i use this method with my frequency counter, it shows 433.92Mhz (or thereabouts) on the display.
Is it possible to manually prompt the device to transmit a report. I guess it would be difficult to diagnose if the data only got sent out once every ten minutes or something.
I take it the blue wires at the designator "RT" on the board go to a thermistor sensor? If the unit only transmits reports on temperature changes, i guess you could heat up then cool down the sensor.