The red LED flashes when properly assembled every 53 seconds, and so symbolizes the operability.
The battery is firmly installed, but since a battery life of 10 years (I could not test ;-)) is specified is that okay.
In addition allows the function by pressing and holding check the single key. This is acknowledged by the shrill beeping unmistakable.
You function in case of fire, I could not yet assess fortunately.
CONCLUSION
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Thus far only good features at a very fair price - therefore a strong buy recommendation! :-)