Self-bondage locks can not only be used to release you directly but also to release keys. This way, you have more choices which cuffs to take.
There are many ways to „lock“ a key away for a period of time. You can hang two ends of a chord in a glass of water and put it in a freezer. Then you attach one end to the ceiling and the other end to the key. After a certain amount of time, the key will fall to the ground and serve as a release of your ties.
Another option is the smart phone release. You put the key with an additional weight on the edge of a table and put your smart phone on it, so it is almost falling. Program a vibration alarm. Once it starts, the key will fall.
Both methods have the same downside: they are not 100% safe to use because either the time is not easy to calculate (8 hours rather than 2 because of too much ice for example) or because it may fail completely (running system crashes).
Conclusion: You better use self-bondage locks designed for that purpose and make them release your key.
Ice locks for example have a very predictable locking time which differs not more than half an hour under comparable conditions. Magnetic time locks can be programmed precisely using a timer and will release the key as soon as the external battery is empty.
Nevertheless, you have to consider some aspects. Speaking about the ice lock, the weight added to the key has to be big enough, so it is falling for sure. Test it several times before your bondage session and then add some weight to be sure. Make sure, the weight can’t hurt you when falling.
The use of the magnetic time lock is easier. Just put the loop plate away and hold the key ring to the bare magnet when powered on and it will hold it well. The key should not be too lightweight anyhow, because there can be some residual magnetic force when power is cut. You can switch the magnet on for half an hour and then cut the power to see wether the key is falling or not. Maybe you will need to attach an additional weight. Again, make sure, the weight can’t hurt you when falling.
One idea at the end: Put on a chastity device and tie your feet. Now, put the keys away using the MagBound. Take a big battery pack like 8000 or 10000 mAh (for 10 hours and more). Now you are still free to move while not being free to do what you like.
In general, following rules apply to key releases:
You have to do you bondage in a way, that you can reach the key once it is fallen and use (!) it. Numb hands or tight handcuffs behind your back are not the best starting situations to get free.
Please consider all safety rules about self-bondage. Tell people to look after you and always use a back-up release!