The EL005 does not have an internal alarm: if you need an audible alarm, connect an EL006 audible alarm unit to the network.
The EL005 logger has internal re-chargeable batteries. These batteries are kept topped up whilst mains power is available, and will keep the system running for up to 72 hours during a mains power failure. The EL018 dialer adapter/battery backup can provide power to the system for much longer periods in the event of mains failure.