you can track fields with track_visibility property.

class claim_submitted(osv.osv):

_name = "claim_submitted"

_description = "claims submitted"

_inherit = ['mail.thread', 'ir.needaction_mixin']

_columns = { 'note':fields.text('Description'),

'verified_id':fields.many2one('res.users','Verified employee'),

'verified_date':fields.date('Verified date:'),

'approved_id':fields.many2one('res.users','Verified employee'),

'approved_date':fields.date('Approved date:'),

'cancelled_id':fields.many2one('res.users','Verified employee'),

'cancel_date':fields.date('Cancellation date:'),

'state': fields.selection([

('draft', 'Draft'),

('verify', 'Verified'),

('cancel', 'Cancelled'),

('done', 'Approved')],

'Status',

readonly=True, track_visibility='onchange',),

}

this will track the field status if the value in the field is changed