How to safely store my locker key in a hostel at night?

Personally I use the pillowcase method. Small torch, asthma inhaler, old phone I use as an alarm/music player (vibrate wakes me, doesn't wake anyone else, best ever), and locker key, all fit into a corner leaving the rest for me to use. Anyone wants in and they're going to need to physically move me and I'm not going to sleep through that.

A quick trick, you know how on your pillowcase there's generally a folded side to stop the pillow sliding out? Put that on the bottom and now even in your worst sleep where you move around a lot your stuff is only going to slide down into that pocket and stay in the case. And my head is in the middle of the case, so things also need to get past my head.

It's not 100%, deep sleeper and someone could theoretically cut the case, but nothing is guaranteed and this hasn't yet failed me in around nine months ish of hostel usage over a year or so; from party mad 32 bed dorms to dingy 6 bed cash only hovels to saner 3 - 4 bed rooms with 24/hr staffed receptions. Traveling is personal though so if you usually wear a chain or necklace while sleeping then sliding a key onto that is simpler. Others have a bag with them on the bed, works great on bunk beds placed around the centre next to a wall as someone's going to need to climb onto the bed to get to it, but I hate that method as it takes away valuable stretch room and pillowcases are a bit more versatile.

You can also use an ankle pouch, I dislike that method though as after a day of walking I don't want anything on my feet/ankles. Or a waist pouch if that feels better, I use that as a backup for when I'm away from a pillow, though if you move around at night on a bed then it can twist and be annoying.

As for phones, I cheat a little. Get a cheap USB battery pack and charge that while you sleep. Get up, attach it to your phone, and you have a charged phone with negligible risk. You can even leave it at the hostel during the day and throw it in the pillowcase as well if it's small enough. And if that gets stolen then 1) it's cheap enough to not matter and 2) you know to only charge things while you're physically there.

And a little niggle from someone who worked as a locksmith for a while: Not all combination padlocks are bad and they have their own advantages. No keyway makes it impossible to pick for instance (epoxy in the front if there is one), and with a three digit code on a twenty or more digit lock there's enough combinations there to deter most people. Get a decent lock, Sargent and Greenleaf 8077 for instance (my favourite convenience lock), and shimming is going to be ridiculously hard as well. With shrouds so is using a bolt cutter so don't forget your combination. From a usability point of view combination locks excel since there's no key to take care of. Swimming pool? Junk in locker, combo lock on, nothing to carry with you. Ditto for a beach or the like.

Even if you prefer locks with keys, and they make up for the lack of convenience with daunting security, approach your lock purchase like you approached the purchase of the most expensive item you're securing. If you'll spend weeks comparing laptop specs and then drop a few K, a few hours looking at lock features or chatting to a decent locksmith and then spending a hundred dollars on a decent lock securing that laptop is absolutely worth it.

And you know how that page you linked had Master locks as an example of how to beat combination locks? Don't. Buy. Master. Locks.

Like, ever. Just no. They make far too many shoddy products to chance your security to. The only exception is if you want to learn picking, having a Master around is a great confidence booster.

Finally, a little something to start your lock research: Choosing a High Security Lock (YouTube).

How about using a motion alarm app such as this Android one. Then you either put the key inside the back cover if it will fit, or just tape it to the phone if it won't. If anyone tries to move or take your phone, the alarm will go off and hopefully wake you up.

If you're scared of accidentally waking lots of people up, you could perhaps put a similar alarm inside your locker instead.

Alternatively, how about a Bluetooth lock controlled by your phone. Someone would have to get your phone password in order to open your locker.

While I was Hostel hopping through Europe, I obtained an mp3 player arm band that was silly large (free too). It was big enough for me to put around my upper leg and hold on to my key and phone while not being too uncomfortable...kept everything safe and unless someone was willing to go under my blanket in search of it, it wasn't being found.

I also purchased a USB battery pack/flashlight. Let me be a bit more flexible with charging the phone so I didn't need to leave it plugged in at night. In the morning during breakfast, I'd have both the phone and battery pack charging for the next day.

Should add a side note. I left the phone on the inside of my leg so I wouldn't roll onto it at night and crush anything.

Put the key under your bed's leg, it will keep it safe, unless you're such a deep sleeper that someone could steal your bed without you noticing.

That's what I do whenever I have to stay in an hotel room or places alike, obviously I'm talking about a regular key, just lift the bed and put the key under one of the bed's leg, it's safer if you use one of the legs on the wall side.

Perhaps you can hide the key under some other furniture available too.

Do I have to draw a sketch?

The best practice is not to store the key in the first place. EG use a combination lock!

You can't lose a key you don't have. And as has been previously mentioned a lock will only keep out honest people.

And for peoples edification .. Opening a key pad lock by tapping it with a small hammer

If the key doesn't have a keyring, you could place it in a moneybelt, and wear the belt at night. You might want two belts, one for night and one for other valuables during the day.

Another possibility would be to leave the key at the hostels reception desk (and ask them to give you a voucher). This way the key is stored in a different area than your room, and in the case that someone does steal your items, you yourself will not be responsible and may be able to get the hostel to reimburse your losses.

In the scenario where you are only worried about a key you can tape the key to you foot or arm with plasters or surgical tape.

Taped to your foot while you are in a sleeping bag would be a very tricky place for a thief to get to without you noticing.

My sleeping bag has a small pocket on the inside, precisely for this kind of thing. But a chain round your neck (or a wristband) works fine too.

Beyond this point you are getting to the level of someone who is prepared to rob you even if you wake up, so your answer here is the same as ever: be prepared to lose it, and get travel insurance.

You could wear socks while sleeping and put the key in one of them. If someone really wanted to get the key they could probably do so by cutting around the key with a razor blade, but it would be a slow, delicate and rather risky manoeuvre to pull off in the dark.