On the lateral side, you’ll be able to identify a small cover which, when removed, will reveal a dedicated space for inserting the two batteries. The device is available as a battery only model and, unlike the PRC710 which has a sealed battery, the First Alert SCO501CN 3ST allows you to change the batteries as soon as necessary it requires 2 AA batteries – the negative aspect is that unlike the sealed batteries which can go up to 10 years which is usually the life expectancy of the smoke alarm, the removable type of batteries will last a lot less. The case of the SCO501CN 3ST is a bit more slimmer than the usual bulky smoke detectors, while maintaining an average diameter it measures 5. 0 x 5. 0 x 2. 0 inches, so, it may fit nicely even in the living room although some may not appreciate the slight industrial look of the device.