Timers.

[jusme]

On a serious note not that I'd bother buying one but if you use a trolley surely this is ideal as it's magnetic to and £2 including the delivery

https://www.amazon.co.uk/dp/B00URCOR1E/ref=cm_sw_r_cp_apa_i_0kriDbMJ5QGCX

As stated earlier - I bought 7 of these and they cost less than £1 each (from china discount stores - can't remember the name) Magnetes not strong enough to secure to trolleys. Clips work fine