A Remote 'doorbell' To Carry On The Person

[kia cat]

Hi I work in a large supermarket. It closes overnight, but staff are still working through the night (Radio on, headphones on etc). A lot of day staff start around 4 am, when the doors are still locked. we need a way to alert the key carrier that staff are waiting to get in.
Any ideas on a remote door chime that can be carried. the store size is about 100K sq ft largest distance from entrance is approx 140m. Hope that makes sense. Thx all ;)

[Zacs-Master]

Mobile phone?

[sandyRoe]

Has the key holder a mobile phone?

[Old_Geezer]

I know you can get wireless repeaters, which given a large enough pocket ....

But 140m seems quite a lot to me. might need to repeated more than once ?

[TonyV]

ask key carrier to be at door at around 4 am. Does key carrier have to lock up after each member of staff enters or is key passed on from entrant too entrant?

[Obiter]

I do not know which 'supermarket' you work for, but in my opinion if they can't set up a device to alert senior staff as to the entry of junior staff, then I would not be shopping there.

[THECORBYLOON]

This'll do for up to 200m http://www.mrdoorbell.com/Friedland-Libra-Wireless-200m-Portable-Door-Bell-Chime-Kit-D914-p-114.html

[anneasquith]

a site called mr. doorbell, fabulous :)

[queen 1954]

in the supermarket i work in the staff are not allowed to use headphones etc on nigtshift because should the fire alarm go off they may not hear it.