Why does the Garmin CIRQA use the older Elevate Gen 4 sensor?

Garmin says the Gen 5 sensor would have made the module thicker. That explanation is hard to square with Garmin’s own Index Sleep Monitor, which carries Gen 5 at 7.8mm against the CIRQA’s 9mm. The likelier reasons are cost and battery draw, since Gen 4 is cheaper and draws less power, which suits a $199.99 band with a ten-day battery.

Is the Garmin CIRQA less accurate because of the Gen 4 sensor?

Not necessarily. Fit, placement and movement affect optical readings as much as sensor generation, and the CIRQA’s Gen 4 has been modified to add skin temperature. Published Gen 4 versus Gen 5 comparisons predate this variant, so it needs its own testing.

How thick is the Garmin CIRQA compared to the Index Sleep Monitor?

The CIRQA module is 9mm thick. The Index Sleep Monitor is 7.8mm thick and uses the newer Elevate Gen 5 sensor. The Index Sleep Monitor pod is also wider, which allows a thinner build for the same internals.