How do loyalty cards work? Barcodes, etc..

Hey there,

I've recently been thinking of an idea similar to a loyalty card concept, similar to flybuys, everyday rewards etc.. However, I'm having trouble finding out some info on how they work.

For example, you go into say.. Woolworths, buy $20 worth of stuff, scan your barcoded everyday rewards card, and no doubt Woolworths have that information on their system, to use as a database for what clients buy (i've read this during my research) .. But obviously, If you were to use the everyday rewards card at coles, nothing would happen during the scan? Similar to using a price attack card at big W ... You see my point.

I'm wondering what is involved in a card that works, at all places? The idea probably isn't that new, and probably would've been done if it was possible, but some discussion would be helpful.

I understand the idea is similar to, a visa vard? Mastercard? They work on all eftpos terminals.. But is it possible to scan/swipe a 'personal' card and have any information transmit to a remote server? For example..

When you buy something at Woolworths, the info from your everyday rewards card will go onto Woolworths internal system, hence surely it wouldn't work at JB-Hi FI, different systems, unrecognized cards etc.. So, is it possible to scan or swipe a card of your own making, and have the information from the transaction sent to a different database... Probably not, right?

I've asked some people about this, I guess some obvious questions are.. Shops wont want you scanning your 'own' card for your 'own' purposes.. It's time consuming, has no benefit to them, etc.. Maybe could cause an error on their system? I don't know..

Anyway, would love to hear from some people who have dealt with loyatly cards, servers, etc... Thanks!