That's the frequency, Kenneth
Compo answers, and some form of explanation
This was the only device not shown in situ, mainly because once deployed it lives inside a cat. It's a radio tag which responds to a query at 130KHz with a number designed to reunite lost animals (or their corpses) with their owners. It is also used daily, at least, to unlock the cat flap for resident (and registered) felines.
Despite the far-from-obvious application, around half of you got the moggy-penetrating frequency spot on.
Phones didn't always have GPS built in, so this Bluetooth accessory from Motorola was designed to provide location information to such handsets. That means it receives GPS information (between 1.1 and 1.5GHz) but communicates over Bluetooth at 2.4GHz. Given the breadth of GPS bands we decided not to list them as an option, so 2.4GHz was the correct answer.
This one is a Bionaire heater remote thermostat, designed to monitor the temperature where you are rather than where the heater is. It's a nice idea, though not terribly well-executed in this instance as the heaters seem to have real trouble picking up the 433.9MHz signal. That's less surprising given the lack of antenna on the thermometer (compare it to the three antennas on the oil tank above, which operates in the same band).
We'll charitably assume that's why so many of you assumed it would be using something more sensible, and thus only a handful of people got this one right.
Here's another device whose usefulness has waned, but not universally as many people apparently still have babies. Transmitting on 49MHz, it relies on low power to avoid interfering with anything else, which is fine but (as users will already know) that makes it very prone to interference itself.
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