If one indulges in Self-Bondage it is necessary to arrange for the release of the keys after a set delay. I cannot use candles due to smoke detectors so I have developed this method.
Using a power time switch set the desired delay and connect a small soldering iron to the output. Secure the iron where it will not make contact with flammable materials, I use a "Workmate" which for the unknowing is a small framework on which is built a wooden vice.
Around the soon-to-be hot iron is placed a strip of plastic, cut from any plastic bag, to which is tied a long string.
The keys are tied in place so they are easily available, then using the string to the iron they are pulled up out of reach and secured there, so when the electricity is turned on by the timer, the iron heats up, the plastic melts and the string is released which allows the keys to drop to where they are available to set yourself free.

The plastic loop

The iron in its support.

The timer set for three hours.

The instant of release.