'Mala' can be a useful tool for meditation. Why it works: chanting a mantra while passing each bead involves a physical action: grabbing the next bead and passing it. This forces your mind to be alert and engages it in passing the beads. During this state of alertness, your mind hears the mantra in the background. Slowly this repetition with alertness results in concentration and trance. The key here is engaging your mind to be alert by assigning it to do a physical action again and again. This is also possible without a 'mala'. For example, go for a walk in a quiet area. Take a step and repeat the mantra you like. Repeat it over and over. Take a step and chant your mantra. This is much better than sitting and using 'mala' because you are having physical exercise, which releases relaxation hormones in your body that will also bring equanimity and help concentrate faster.
Other ideas: take stairs, climb a step slowly and repeat your mantra;
In a gym, get on a treadmill, synchronize the rhythm of your chanting with the rhythm of walking. For example the mantra finishes in each 3 or 4 or x steps. For example take the mantra 'Namo Arhato', finish it in two steps, observe a break of another two steps, repeat the mantra in next two steps, break of two steps... You can adjust the speed of walking and chanting at your convenience.
In a gym, practice stationary bike, synchronize the rhythm of your chanting with the rhythm of peddling.
Close your eyes and clap gently and repeat a mantra.
Close your eyes, breath gently and repeat a mantra with each breath in/out.
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Mala or no mala, you can get the benefit of this technique anytime anywhere.