Latching Relay

I am putting together a project which is designed around low power DC
(battery driven), and that ultimately results in a high (+5v) or low
(0v/ground) - a simple change of state to pin out of IC. I have good
control over this output, and can provide assertion high or low, or
indeed momentary.

I intend to then couple this output through a darlington transistor
pair to provide the necessary current for a relay to then switch mains
power and operate a mains powered device (eg. a light bulb).

The problem I have is:
As the project is battery driven, I MUST be as frugal as possible with
current drain. I cannot afford any power drain from the battery when
the relay is in operation and the mains powered device is on.

What I have considered:
Latching relay - I think these work by providing a brief trigger to
energise the coil, the n/o contact is somehow strapped to the load
side, which then latches the relay on after trigger. Reset would
require a break in the coil leg to ground/0v. Have I understood this
correctly? Will there be no further drain from battery after initial
trigger?

This initially appear the answer, but as my output is from 1 IC pin
only (high, low or blip), I am left wondering how to design my cct to
trigger and re-set the relay?

Magnetic latching relay - this looks like a strong possibility. I could
set my output to momentary, then each time pin assertion, the relay is
triggered and toggled on or off. I believe because these relay on
magnets, that they do not use or require current to maintain state?

I don't understand the above working designs / options of these relays
enough to be confident within my design, could someone help me with my
understanding and perhaps make comment to my original project
requirement (ie. battery control, switch on/off of mains power, no
battery draw when coil/switch is energised).

MANY thanks,

Ian.

.

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